THOUGHTS ABOUT A SCIENCE OF EVIDENCE
I have been pleased and honoured to be associated with a project at University College London [UCL] entitled:Evidence, Inference and Inquiry: Towards an Integrated Science of Evidence
. This project, now enjoying the support of theLeverhulme Foundation
and theEconomics and Social Research Council
, was initiated and is so capably directed by Professor A. Philip Dawid. This project currently involves the active collaboration of persons from a wide array of disciplines at UCL including probability and statistics [Phil Dawid's discipline], law, medicine, geography, education, philosophy, ancient history, economics, psychology, and computer science. Persons involved in the generation, analysis and application of ideas in any area of study have obvious interests in the study of evidence.
Explanations and understanding of phenomena they encounter in these activities are grounded on evidence. There is no single discipline that forms the repository of all knowledge regarding the evidential foundations of reasoning. However, the field of law in our Anglo-American judicial system has supplied us with the oldest and perhaps the most extensive recorded legacy of experience and scholarship on evidence. We have so much to learn about evidence from each other and Phil Dawid's project is designed to stimulate and enhance this learning process. The wordintegrated
in the title of this project acknowledges the importance of obtaining knowledge about evidential issues as they are encountered across disciplines and then combining and sharing this knowledge in useful ways.
As our work progressed it seemed obvious, from the title of our project, that we would eventually find it necessary to say what is meant by ascience of evidence
. As obvious as this requirement appears, there is nothing easy about satisfying it. What follows is my own attempt to identify what a science of evidence is or might become, what its proper domain and methods of study might be, and what it might contribute in the way of insights about evidence that are useful and helpful to all of us, regardless of our interests. I am under no illusion that my thoughts about such matters will escape criticism. I hasten to emphasize at the outset that my account of a science of evidence does not represent any consensus view reached by those of us involved in our UCL studies. In truth, as far as I can tell from our discussions, there has never been any attempt to reach consensus on this matter. All I can promise in my account of a science of evidence is that it will not exclude persons in any area having interests in the properties, uses and discovery of evidence, who might have valuable insights about evidence to contribute, or who might encounter evidential issues that can be addressed in at least potentially useful ways by such a science.
Defining ascience of evidence
is complicated by the necessity of defining the key wordsevidence
andscience
. Defining the wordevidence
is not so easy, as I discovered some years ago
Defining the wordscience
is not so easy either as we observe while examining shelf after shelf of books and papers on the topic of science, what it is or is not, its various alleged methodologies, and its accomplishments. Even talking about a "science" of evidence can arouse controversy. In fact, some colleagues have argued that we should drop the word "science" and simply say that our work involves the "study" of evidence. There are several reasons for discontent about use of the term "science". Many persons whose work requires consideration of the properties, uses and discovery of evidence would not wish to identify their work with science. In addition, we hear arguments that science alone, often made with reference to the physical sciences, can produce conclusions from evidence that can be taken seriously. Allegedly, conclusions reached from evidence by the rest of us are deficient in various ways. One of the ranking examples of an attempt to disparage the work of colleagues in other disciplines came from the physicist Lord Rutherford who said that all science was either physics or stamp collecting. Taken seriously, this leaves the work that most of us do as being equivalent to stamp collecting. But there is a footnote to this story about Rutherford. It happens that he received his Nobel Laureate in chemistry and not in physics
But I also know that I cannot escape controversy in my attempt to be unrestrictive in a search for knowledge about evidence from whatever source it may come. It might be argued that we are all experts regarding evidence since each one of us makes use of it every day of our lives. However, there are many people who will accept as evidence, about events of concern to them, information that is provided in horoscopes, by psychics, or by televangelists. In America at present we often hear about governmental decisions that are "faith-based" rather then "evidence-based". In some instances a person might report that a conclusion or a decision was based on a revelation from God, or was based on information provided in ancient documents such as the Bible, the Koran or the Talmud. A fair question concerns the credentials, as evidence, of information provided from sources such as those just mentioned. An appropriately identified science of evidence might, at the very least, make us all better informed about the evidential basis for inferences and decisions of concern to us.
So, the above difficulties acknowledged, I will begin my attempt to describe a science of evidence. But I must first tell you briefly about the standpoint or frame of reference from which I have approached this task.
1.0 A STANDPOINT IN THIS ACCOUNT OF A SCIENCE OF EVIDENCE
I have no difficulty at all in recalling the many things I have already learned by my association with two persons also involved in our current
UCL project on evidence. My contact with Professors William Twining [UCL] and Terence Anderson [University of Miami, Florida] now goes back almost twenty-five years. They are renowned scholars, educators and practitioners in the field of law. My training happens to be in the fields of psychology and mathematics. So, I have first-hand experience regarding the benefits of cross-disciplinary interactions. What initially brought the three of us together was our common interest in the work of John H. Wigmore, the American legal scholar who is arguably one of the most profound persons who ever wrote about evidence and proof. My discovery in 1970 of Wigmore's works led me to begin exploring the rich legacy of experience and scholarship on evidence to be found in the field of law. Shortly thereafter I began an attempt to bring this rich legacy to the attention of persons in many other disciplines who I believed would profit from their exposure to this legacy.
My contact with Twining and Anderson began in the early 1980s and has increased steadily since then. I was pleased and honoured more than I can say when they invited me to join them as a co-author in a revision of their very influential work on evidence
The first standpoint element involves my telling you what role I am playing or what "hat" I am wearing in my present account of a science of evidence. In my entire academic career I have been a student of the evidential foundations of probabilistic reasoning. In my role as a student of evidence, studying as many of its subtleties or complexities I could discover, I quickly came to the conclusion that I would need all the help I could obtain, regardless of what disciplines or persons it came from. As I noted above, there is no single discipline known to me that provides all answers regarding the properties, uses and discovery of evidence. A bit later I will mention William Twining's assertion that a science of evidence must be interdisciplinary in nature
The second element involves my specifying at what stage in what process am I. I have two responses here. The first concerns my career-long interest in the study of evidence. As far as this process is concerned, at age 73 I guess I will have to admit that I am in the latter stages of it. As far as the process of describing a science of evidence is concerned, I am in the early stages of it. Though I did make reference to a science of evidence in a previous work
A most important standpoint element is a declaration of one's objectives in the analysis presented. As I have already announced, my objective in this present work is to identify what a science of evidence is or might become, what its proper domain and methods of study might be, and what it might contribute in the way of insights about evidence that are useful and helpful to all of us regardless of our interests. I add here the following related concern. Suppose you are convinced that there is such a thing as a science of evidence; should you care? Part of my burden in this present work is to provide reasons for a widespread interest in such a science that I believe will be of great assistance even to those who will continue to object to my use of the term "science".
Finally, I must also tell you about the materials to which I had access in my present account of a science of evidence. This question is easily answered; I have had a wealth of information to draw upon coming from a wide array of disciplines in which there has been interest in the properties, uses and discovery of evidence. Some of this information is very recent and comes from a meeting held at UCL on 7 June, 2005 during which some of my ideas about evidence were challenged. This meeting set off a vibrant subsequent exchange of views via e-mail that have been carefully recorded and distributed by Jason Davies and Steve Rowland
So, these standpoint questions now put on the table, I can begin by telling you what I know about the first persons who entertained thoughts about a science of evidence. I first heard about a science of evidence from a rather unlikely source.
2.0 SOME BEGINNINGS
Israel Zangwill [1864 - 1926] was no scientist, philosopher or logician. Educated at the Jews' Free School and at the University of London, he became a novelist, playwright and Zionist leader. Among his many published works is a mystery story he wrote in 1891 entitledThe Big Bow Mystery
. This story, that Zangwill admits was inspired by Edgar Allen Poe's mystery stories, is the first in what are calledlocked room stories
. In these stories a crime is committed in a room locked from the inside and so it becomes nearly impossible to tell who committed it. In this story we are introduced to a retired police investigator named Mr. George Grodman who has some reputation as an investigator who solves cases with logic and evidence. Of course Grodman brings Sherlock Holmes to mind. As Holmes frequently expressed his contempt for the abilities of Inspector Lestrade of Scotland Yard, so Grodman was also contemptuous of the abilities of a Scotland Yard detective named Edward Wimp.
At a late stage in Grodman's investigation of a murder committed in a locked room, he is asked to state his findings to the Home Secretary. Grodman begins
"Pray do not consider me impertinent, but have you ever given any attention to the science of evidence?"
"How do you mean", asked the Home Secretary, rather puzzled, adding with a melancholy smile, "I have had to do so, lately. Of course I've never been a criminal lawyer, like some of my predecessors. But I should hardly speak of it as a science. I look upon it as a question of common-sense". "Pardon me, sir.
It is the most subtle and difficult of all the sciences. It is, indeed, rather the science of the sciences. What is the whole of inductive logic, as laid down, say, by Bacon and Mill, but an attempt to appraise the value of evidence, the said evidence being the trails left by the Creator, so to speak?. The Creator has - I say it in all reverence - drawn a myriad red herrings across the track, but the true scientist refuses to be baffled by superficial appearances in detecting the secrets of nature. The vulgar herd catches at the gross apparent fact, but the man of insight knows that what lies on the surface does lie."
My first reading of Mr. Grodman's comments about a science of evidence was not in theBig Bow Mystery
itself; I only read this mystery story much later. I first saw Grodman's comment, that appears in slightly reduced form, as the frontispiece of Wigmore'sScience of Judicial Proof
Wigmore'snovum organum
for the study of evidence and proof has application in any area in which we have the task of drawing conclusions from masses of evidence. The title of his work announces that it is based on logic, psychology and general experience. I have no doubt that Wigmore believed his analytic and synthetic methods of making sense out of masses of evidence were applicable in any area; he just illustrated their use in judicial trials, the area in which he had the greatest interest. In tracing Wigmore's intellectual lineage we find a connection at UCL in the person of Jeremy Bentham [1748 - 1832]. In William Twining's analysis of Bentham's and Wigmore's theories of evidence, he argues that, as a theorist of evidence, Wigmore is a direct lineal descendent of Bentham
Their primary concern was to introduce system, clarity, simplicity, efficiency and above all rationality into the field of evidence. Both saw the study of evidence as a fit study for scientific treatment; even more important they saw factual inquiries in adjudication as being a standard example of factual inquiries in general, the peculiar conditions and constraints of litigation being but secondary. Their common starting point is a general theory of belief in the context of all factual inquiries.
I note here that Mr. Grodman, speaking with all due reverence, says that we all have the task of appraising the value of evidence in the trails left by the Creator who, unfortunately, has also drawn a myriad of red herrings across these trails. In our various disciplines, each of us follows many different trails and we also encounter the many red herrings that have been left across the trails we follow in the inferences and decisions of interest to us. It seems clear that Wigmore, and Bentham before him, were concerned about a science of evidence and proof that would allow us better means for following our trails while avoiding the red herrings we so often find in our searches for the secrets of nature. Wigmore noted that although the field of logic supplies us with many canons for the simplest cases of reasoning, they have not provided us with methods for reasoning based on masses of what he termedmixed evidence
Wigmore's hope in hisnovum organum
for the study of evidence was to advance the study of proof based on evidence in the complex situations we routinely encounter such as in the field of law. As he noted
For one thing, there is, and theremust
be, a probative science - the principles of proof - independent of the artificial rules of procedure; hence it can be and should be studied. This science, to be sure, may as yet be imperfectly formulated. But all the more need is there to begin in earnest to investigate and develop it.
It is fair to say that Wigmore made as many advances in a science of evidence and proof as any person who thought about such a science. But I believe that there have been a variety of advancements toward a science of evidence since Wigmore's time. These advancements have come from persons in many disciplines.
I have often thought it interesting that a science of evidence, as the science of science, should have been proposed by the fictional literary character Mr. Grodman. Perhaps this possibility would have been more widely discussed if it had been proposed by the more well-known character Sherlock Holmes. The observational, interrogative, imaginative and inferential capabilities that Conan Doyle provided Holmes have been very often cited in discussions of the properties, uses and discovery of evidence by persons in many disciplines. There have been other thoughts about what would constitute a "science of science", a good example being those of the eminent biologist Ernst Mayr
3.0 CONCEPTS OF EVIDENCE AND SCIENCE: THEIR EMERGENCE AND MUTATION
My analysis of a science of evidence would quite inadequate if I gave no attention to how the concepts ofevidence
andscience
have emerged and changed over the ages. I understand that appropriate study of the emergence and mutation of these concepts has occupied the attentions of a great many persons having interests in these matters. Here I come to the first of the selectivity problems I earlier said I faced. I have chosen to mention the works of others that I believed would be of assistance in my stated objectives concerning what a science of evidence might involve, what methods it might employ, and who might benefit from drawing upon this science. I have so far given only the briefest account of the meanings of the two termsevidence
andscience
that I seek to relate. I hope that the following discussion, though embarrassingly brief, will be adequate in acknowledging the kinds of issues we ought to keep in mind in any discussion of a science of evidence.
3.1 On the Concept of Evidence.
We might take as a starting point the obvious fact that we have used information provided by our senses as evidence in drawing conclusions and making choices throughout our history as a species. Information provided by our visual, auditory, tactual, gustatory, olfactory, and proprioceptive or kinaesthetic senses has ensured our survival as a species. The same might of course be said about the role of sensory evidence in the survival of other species. The fact that we have employed evidence throughout our entire history is acknowledged by James Allen in his careful analysis of ancient debates about the nature of evidence
Allen goes on to tell us that it was Cicero [Marcus Tulliius, 106 - 43 BCE] who first introduced the termevidentia
, as a Latin rendering of the Greek wordeuargeia, meaning the quality of being evident
…historians are left forever chasing shadows, painfully aware of their inability ever to reconstruct a dead world in its completeness, however revealing their documentation. … We are doomed to be forever hailing someone who has just gone around the corner and out of earshot.
In the same way, the intelligence analyst attempting to predict possible terrorist activities at some time in the future cannot observe these activities since they have not happened yet. This person can only use as evidence in such predictions observable indicators of the capabilities and intentions of groups or individuals who might be involved in such activities.
Leaving the ancient Greeks and Romans, it is frequently said that civilization in the West entered upon what is commonly called "the dark ages". These ages may have been dark in the West, but they were anything but dark in cultures in the Middle East, in India and in China. Though specific scholarship on evidence is hard to find in these early cultures, the advancements they made in science and technology are indeed impressive, though they are often slighted in Western accounts of the history of science. The advancements made in these cultures certainly points toward their great sophistication in understanding the role of evidence in the advancements they made.
Returning to " the dark ages" in civilization in the West, I first draw upon the insights of Ian Hacking who has provided an account of forms of evidence sanctioned in this period, which he said lasted for a very long time
I have found a bit of fault with Hacking's account of how rejection of tangible evidence, in the form of observable signs of nature, retarded progress in inductive reasoning. He fails to mention the emergence of activities that were taking place in the early years of Oxford University that helped set the stage for methods by which we put questions to nature in the form of experiments we design and carry out. To set the stage for a discussion of the heroism it took to begin the process of relying on tangible evidence from nature, I draw upon a comment in a work by William and Martha Kneale, who said
The chief obstacle to steady scientific progress was not the influence of Aristotelian logic or anything else derived from Greece, but the lack of sustained curiosity about things which were not mentioned by ancient authors and did not appear to contribute in any way to salvation. It was easier to get the support of the Pope for aninquisitio haereticae pravitatis
[an inquiry into the depravity of heretics] than for aninquisitio naturae
[an inquiry of nature]. (Translations my own).
The penalties for going against the accepted teachings of the church were indeed severe, as several of the persons I now mention discovered for themselves. The four persons I mention were all at Oxford, and some were at various times in Paris: Robert Grosseteste [1168 - 1253], Roger Bacon [1214 - 1292], John Duns Scotus [1265 - 1308}, and William of Ockham [1280 - 1349]. Their activities are an important part of any story about the emergence of the concept of evidence since they all either developed or were aware of empirical evidential methods for isolating causes for the phenomena we observe in nature. Six centuries later, John Stuart Mill was credited for their discovery. We all hear about "Mill's Methods" but rarely do we hear about the persons who appear to have been the first to have discovered them.
The next part of my story about the emergence of the concept of evidence takes us to the field of law in England at the same time period as lived the four Oxford scholars just mentioned. What I have claimed as the rich legacy of experience and scholarship on evidence in the field of law certainly had an unpromising beginning. In these times a defendant charged with a crime had the burden ofproving his innocence
. The following sequence of events occurred: judgment, trial and sentence. At the judgment stage the defendant was given the option of which of three methods would be employed to prove his/her innocence. There was a noticeable absence of evidence in these three methods of proof: trial by combat, various ordeals such as carrying a hot iron, and oaths taken on behalf of the accused by various numbers of people. Proof by all of these methods was left to the judgment of God [judicium Dei
]. The argument was that God would not side with the guilty party in a trial by combat; God would not allow the burnt hand of a guilty defendant to heal in a certain short period of time; and God would strike dead any person who gave a false oath on behalf of the defendant.
The history of how these evidence-free methods of proof were replaced, gradually, by a jury system is recorded in a number of valuable and interesting works
Just when jurors ceased to be witnesses and began to take on the role of disinterested or unbiased persons who assess the credibility and force of evidence given by external witnesses is a controversial issue. In any case the process was gradual. Wells notes the importance of a statute of Edward III in 1352 that allowed the accused to challenge the suitability of any juror who had joined in his/her indictment
But there were many bumps along the road to the development of the jury system as we know it today. Before 1670 jurors could be attainted, and mistreated in various ways, if they rendered a verdict the crown or the courts said was "against manifest evidence". A landmark case in this year involved the trail of a jury foreman named Edward Bushel who was accused of encouraging a wrongful verdict in the case of the Quakers William Penn and William Mead, who had been charged with inciting to riot in London. The Chief Justice in this case, John Vaughn, ruled that Bushel could not be punished because state control over jury verdicts was as unfair to the jurors as it was to the defendant. Vaughn ruled that courts could not rule on judgments of fact, but jurors could not rule on questions of law. Thus, we have the division of labour among judges and jurors that, for the most part, exists today. Jurors rule on issues concerning the credibility and probative force of evidence, although judges rule on the relevance and admissibility of evidence.
As the rights of an accused to representation by an advocate became more extensive, the process became truly adversarial in nature. In this adversarial climate it is to be expected that one side of the matter in dispute will meticulously, and often ruthlessly, examine the evidence and arguments provided by the other. It was here that concern about so many evidential issues arose in our Anglo-American legal system. The adversarial nature of our system led to an often-cited quotation by Sir Matthew Hale who said that questioning by the parties in contention, by the advocates, judges and juries is a better process for "beating and boulting the truth" than any other system lacking this adversarial quality
I now leave the field of law by noting William Twining's discussion of what he terms therationalist tradition
of evidence scholarship in our Anglo - American legal system
Probability presents a paradox in the sense that it has a very long past but a very short history. Florence David tells us about objects resembling dice that were possibly used by paleolithic peoples in gambling games, but more likely used as devices for foretelling events in the future
Emerging interest in probability calculations brought an emergence of interest in calculations associated with certain evidential situations, a good example being what were calledcredibility-testimony problems
. One such problem involves what was calledsimultaneous testimony
or what we would today callcorroborative testimony
. Suppose n independent witnesses who all tell us that event E has occurred where each of these witnesses has probability p of "speaking the truth". Our interest concerns P(E) following each of the testimonies of these n witnesses who all say the same thing. Another problem addressed in these early works was what was calledsuccessive testimony
or what we would refer to today assecond-hand
orhearsay
evidence. In this case we have a chain of human sources through which a report is passed where it is supposed that each source in this chain has probability p of "faithfully transferring this report". Our interest is in determining the probability that this final report is the same as the one described by the initiator of this report. As Keynes notes, early probabilists recognized that the rareness or improbability of the event reported in testimony, in addition to the credibility of sources, has a bearing on the value of testimony
As Daston
Concerning philosophers interested in evidence I begin by giving special attention to the writings of John Locke [1632 - 1704]. In his workAn Essay Concerning Human Understanding
In all views known to me, the force, weight, or strength of evidence is graded in probabilistic terms in one way or another. Locke's degrees of assent represent one early attempt to relate the force of evidence and probability. In my early work on evidence I became interested in generating equations, following from Bayes' rule, that represent the process of assessing and grading the force of evidence. I had formed the idea that most inferences from evidence involvechains of reasoning
of various lengths. The first links in such chains concern thecredibility
of the source from which the evidence comes. Later links in a chain involve logical steps in an argument establishing therelevance
of the observed or reported event on hypotheses or propositions at issue. These relevance links are sources of doubt you believe to be interposed between your evidence and what you are trying to prove or disprove from it. At the time, we called these chains of reasoningcascaded
,multistage
, orhierarchical
inferences. When I began to read Wigmore, I quickly observed that he had already recognized the fact that inferences from evidence involve arguments or chains of reasoning, often having many links. He used the termcatenated inference
to refer to such chains of reasoning
There is an interesting connection between Wigmore and the philosopher Stephen Toulmin. In a very influential work Toulmin described the essential ingredients of arguments based on evidence and how they are related
When I first started my studies of evidence my experience was much the same as the one Wigmore recorded. I could find nothing in the literature in philosophy, or probability, on chains of reasoning, or inference networks, particularly those based on various forms and combinations of evidence. As Wigmore noted
The logicians have furnished us in plenty with canons of reasoning for specific single inferences; but for a mass of contentious evidence in judicial trials, they have offered no system.
But I believe Wigmore would certainly have great interest in works on evidence by philosophers that have appeared since his time. I refer especially to the works on evidence of Peter Achinstein. In an edited collection of works by several other philosophers Achinstein provides a variety of thoughts on such issues as what qualifies as evidence, what constitutes relevant evidence, what is the role of confirming and conflicting evidence, and what is the role of evidence in the process of discovery
It seems that Achintsein's edited collection of papers in 1983 provided just an introduction to his recent and more extensive work on evidence
It is to be expected that there are standpoint differences between philosophers and persons in other areas, such as law, in their studies of the complexities of evidence. As a result, different people will ask different questions about the properties, uses and discovery of evidence. If I had had access in the 1960s to Achinstein's 2001 book it is very likely that I would not have appreciated it. The main reason is that I was asking questions about evidence that Achinstein does not answer. I did find answers to these questions in works describing the centuries-old record of experience and scholarship in the field of law. Further, I came to believe that the answers to these questions apply in virtually every other context, I will return to Achinstein's most valuable thoughts about evidence when I seek to defend the idea of a science of evidence.
At our meeting at UCL on 7 June, 2005 someone mentioned that a science of evidence would only be just a part of epistemology. But any science you care to identify is also part of epistemology. The wordscience
comes from the Latin wordscientia
meaning knowledge. As we know, epistemology is the study of the nature of knowledge and how we justify it.
It is certainly true that most issues arising in the study of evidence have roots in epistemology. We may easily say that we have evidence about a certain event, but whether we haveknowledge
about this event is a more difficult matter. As an example, suppose we wonder whether or not event E happened. You say: "Let us ask person P, she willknow
whether E happened or not." So we ask P if event E occurred and she says that it did occur. Two basic questions we now have are: 1) How do we tell whether Pknows
that E occurred?; and 2) Do we ourselvesknow
that event E occurred as a result of P telling us that it did occur?
Epistemological issues are inescapable in studies of the credibility or believability of evidence. In the case of testimonial evidence from human sources, we have theircompetence
as well as theircredibility
to consider.
A competent source is one who had access to the event she/he reports or who made a relevant observation of this event, and one who also had some understanding of what was being observed. Human source credibility rests on other attributes such as veracity, objectivity and observational accuracy. The trouble is that competence does not entail credibility, and credibility does not entail competence.
Unfortunately, some persons confuse competence with credibility often with disastrous results. Here is a human source who did in fact make a relevant observation but who is untruthful in reporting the results of this observation. I will return to these matters in Section 4.2.2 when I consider epistemological issues that arise when we attempt to identify attributes of the credibility or believability of evidence.
I leave my account of how the concept of evidence emerged and changed over the ages by returning briefly to the field of semiotics. I mentioned earlier that semioticians could argue that there has already been a science of evidence in existence for millennia, except that they have called it thescience of signs
. For persons troubled by whether a science of evidence would be relevant to their inferential activities or disciplines, semioticians have an easy answer. They will say: "Our work on a science of signs applies to you, regardless of who you are and what work you are doing". Semiotics involves the study of any kind of communicative process and thus includes study of signs, signals, symbols, and codes of any sort as well as the means by which they are produced and understood. Following is one account of how semiotics claims to be the study of everything that might be construed as evidence in the form of any of the signs given to us by nature, as well as study of the process by which we establish the meaning of this evidence.
In addition to his world-wide reputation as a novelist, Umberto Eco is a prominent semiotician and scholar of medieval history. In one of his works
Finally, there is one interest in which semioticians and scholars of evidence do have in common and it concerns the exploits of Sherlock Holmes. For example, in historical scholarship, in probability, in law, and in so many other areas researchers have used examples drawn from one of Holmes' cases to illustrate their concern about some evidential issue. In semiotics there is a very interesting book on the investigative abilities of Holmes and the thoughts of Charles S. Peirce regarding the abductive or imaginative reasoning involved in investigation or discovery
3.2 On the Concept of Science and Its Methods
It is said that necessity is the mother of invention but curiosity is the mother of science. Something we all have in common, regardless of our disciplinary interests, is our curiosity or wonder. If we had no curiosity about past, present or future events and phenomena, whatever they are, we would not be engaged in the research we are doing. Whether any of us will say that this curiosity mother has made us scientists is left for each of us to decide. In defining the word evidence, I said that the OED led me in a circle. This is not the case with the wordscience
, but there is considerable variation in the definition of this word; here are some alternatives the OED provides
Knowledge obtained by study; acquaintance with or mastery of a department of learning.
A particular branch of knowledge or study; a recognized department of learning.
A branch of study that deals either with a connected body of demonstrated truths or with observed facts systematically classified and more or less comprehended by general laws, and which includes reliable methods for the discovery of new truths in its own domain.
The kind of organized knowledge or intellectual activity of which various branches of learning are examples.
The intellectual and practical activity encompassing those branches of study that apply objective scientific method to the phenomena of the physical universe (the natural sciences), and the knowledge so gained.
The OED also includes various definitions of the word science that have been used in the past. For example, the wordscience
was used in the 1500s to refer to a craft or trade; in the 1600s it was used with reference to activities concerned with theory rather then method. Lord Rutherford would be dismayed to learn that the OED has never defined science to be the study of physics.
Our studies of evidence would easily seem to qualify as a science under definitions 1, 2 and 4. But these definitions are quite unrestrictive and might be said to be weaker definitions. Definition 3 is stronger because it supposes a "connected body of demonstrated truths or facts systematically classified" that are "comprehended by general laws". We might easily argue about whether a science of evidence can have these attributes. However, I will later show how evidence can be classified in systematic ways.
I am also less troubled by the requirement in definition 3 concerning reliable methods for the "discovery of new truths". In Section 3 I will attempt to show various ways in which we are able to discover new truths about the properties and uses of evidence. Evidence has many subtleties or complexities that can be exposed by various methods I will discuss. Once exposed, they can be exploited in our inferential and decisional activities. There is a troublesome feature of definition 5. It seems to suppose that there is a unique objective method that applies only in the physical sciences that apparently excludes the rest of us. As I proceed in this section I will draw upon several very well informed persons who will argue that there is no special or unique method in science.
I return briefly to the saying that necessity is the mother of invention and curiosity is the mother of science. I have never put much faith in this saying since it seems very unlikely that people can invent things without having a strong level of curiosity about how some problem might be solved or how something could be made more efficient, easier, or safer. My belief is that curiosity or wonder has been the engine driving the imaginative reasoning underlying both science and invention. In any case, it seems that we were inventors long before we were scientists. A timeline of science constructed by Ochoa and Corey begins around 2,500,000 years ago, with the hominid specieshomo habilis
developing the first stone tools, and ends in the year 1995, the year this timeline was published
I go no farther in my account of concepts in science without dwelling upon the crucial role played by mathematics in scientific discoveries and explanations. We have all heard it said that the amazing thing about mathematics is that it works so well for so many purposes. I have found the following account of mathematics given by the philosopher Carl Hempel to be especially helpful in illustrating the value of mathematics in a science of evidence
But while mathematics in no case contributes anything to the content of our knowledge of empirical matters, it is entirely indispensable as an instrument for the validation and even for the linguistic expression of such knowledge: The majority of the more far-reaching theories in empirical science - including those which lend themselves most eminently to prediction or to practical application - are stated with the help of mathematics; … Furthermore, the scientific test of these theories, the establishment of predictions by means of them, and finally their practical application, all require the deduction, from the general theory, of certain specific consequences; and such deduction would be entirely impossible without the techniques of mathematics which reveal what the given general theory implicitly asserts about a certain special case.
On some accounts I have read, it is said that one criterion for an area being called a "science" is the extent to which this area makes use of mathematics. Mathematics plays several crucial roles in a science of evidence; whether we choose to make use of it or not is another matter. All conclusions reached from evidence are necessarily probabilistic for five reasons. Our evidence is never complete, is usually inconclusive, frequently ambiguous, commonly dissonant to some degree, and comes to us from sources having any gradation of credibility shy of perfection. Probability theories, there are several of concern to us, offer us guidance about how we ought to assess and grade the inferential or probative force of evidence, offer us alternative ways in which we might combine these gradations, and offer us the means for expressing the probabilistic strength of the conclusions we reach. I will return again to the idea that probability is more about arguments than it is about numbers. In the construction of arguments as complex inference networks we are guided by the mathematical theory of graph structures. Both the Wigmorean methods I have mentioned and the newer Bayesian network analyses are consistent with the mathematical requirements of graph structures applied to the analyses of complex inferences. I mention one matter Hempel overlooked in the quote given above that occurs in the study of evidence; it concerns the heuristic merit of mathematics. Certain probabilistic analyses of forms and combinations of evidence we all encounter can prompt us to ask questions about the matters of concern to us that we might never have thought about asking in the absence of such analyses.
I pause here to mention again that one of my major objectives is to consider what methods of study would be appropriate in a science of evidence. My concern of course is to be able to describe methods that all of us could employ, or do now employ, and that we find useful regardless of our inferential and decisional interests. Historical studies of the development of methods in the sciences are interesting, but also vexing in various ways. But so is the history of accounts given in the philosophy of science in which we are told how knowledge is acquired by scientists, how reliable such knowledge can be, and how scientists might do a better job at acquiring knowledge. I left off my historical account of evidence, as far as science is concerned, by mentioning how early Oxford scholars laid some of the foundations for the empirical methods associated with what is frequently referred to as theScientific Renaissance
in Western cultures. I can now bring this account more up to date thanks to the work of a philosopher of science named David Oldroyd [University of New South Wales].
In a seminar on the processes of discovery and invention I offer for engineers, I have found a work of Oldroyd's to be especially useful
The upward arm of this arch is grounded on observations we make, and from them generating new thoughts, in the form of hypotheses, about how these observations are to be explained. I have always associated this upward arm with discovery-related processes in which we seek explanations for observations or signs we observe in nature, whatever they might be. It seems that Galileo, the Port Royal Logicians [Antoine Arnauld and Pierre Nicole], Issac Newton, John Locke, and William Whewell all believed this upward, discovery-related arm involves inductive reasoning. John Herschel, however, was not so sure that new ideas are generated by inductive reasoning. His works seem to have opened discussion on the distinction between the generation or discovery of a hypothesis and the justification of it. But it remained for Charles S. Peirce to suggest that a new form of reasoning, which he calledabduction
[sometimesretroduction
], to account for the imaginative process of generating a new hypothesis. In the caseA Study in Scarlet
, Sherlock Holmes referred to this process asreasoning backwards
The downward arm of Oldroyd's arch concerns the generation of possible evidential tests of a generated hypothesis. This involves part of an attempt to justify this hypothesis. All persons I have mentioned view this process as being essentially deductive in nature. What is interesting is that for so many years philosophers concentrated their interests just on the downward arm involving the justification of a hypothesis. In so many works we hear about thehypothectico-deductive
method of science
. What was so long avoided was the upward discovery-associated arm of the arch of knowledge. Even Hempel in the quote cited above just talks about the deductive generation of tests or predictions from some hypothesis and makes no mention of where this hypothesis came from in the first place. In one of the most curiously titled works I have ever read,The Logic of Scientific Discovery
, Karl Popper advocated what he termed the "elimination of psychologism" from scientific inference. He says nothing about a logic of discovery, relegating it to psychologists. As he stated
The initial stage. the act of conceiving or inventing a theory, seems to me neither to call for logical analysis nor be susceptible of it. The question how it happens that a new idea occurs to a man - whether it is a musical theme, a dramatic conflict, or a scientific theory - may be of interest to empirical psychology, but it is irrelevant to the analysis of scientific knowledge.
The many contemporary philosophers now interested in the process of discovery cannot have taken Popper very seriously.
I have two more names to mention concerning the arch of knowledge, the logicians Jaakko and Merrill Hintikka
Peter Achinstein writes on evidence as I have noted above. But he also writes on methods in science and has given us a valuable collection of excerpts from the works of eminent scientists and philosophers of science regarding methods
But the hypothetico-deductive method has its share of critics, one of whom is the philosopher Derek Gjertsen. He argues that this method does not accurately describe the methodology of science and can readily lead to false conclusions. As he states
Further, the system allows little room for creativity, originality, or even luck.
It is all very like attempts sometimes made by successful novelists and directors of courses on creative writing to lay down rules for the writing of novels. Yet it happens that novels that scrupulously follow the perceived rules can be totally unreadable, and others which violate every maxim in sight can enthrall. Science, no less than painting, cannot be done by numbers.
You will find no shortage of numbered rules for anyone claiming to do science. Here is a current "science by numbers" approach I found recently on the internet. It comes from Edmund Wilson, a well-known marketer of scientific and technological apparatus. Wilson gives us an eleven-step method for the discovery and testing of hypotheses in science
I now direct my attention to those of you who have read this far and are feeling left out in this account of science and its methods. You may be a scholar of ancient history, political thought, education, religion, or in other disciplines in the humanities or the social sciences that are rarely included in discussions of scientific methods. I will ask you to consider the works of several current scholars whose views should be of considerable interest to persons whose research does not involve experimentation of any kind or the employment of other methods so commonly associated in the past with the physical sciences. The first person I will mention is a chemist named Henry H. Bauer. Bauer claims that "the scientific method" is a myth that has caused others, including scientists, educators and the general public, no end of trouble
Indeed, thinking of science as using the scientific method portrays science as an activity that is highly unnatural: human beings are not by nature objective, judicious, disinterested, skeptical, rather, human beings jump to conclusions on flimsy evidence and then defend their beliefs irrationally. The widely held myth
of the scientific method is one reason why scientists are stereotyped as cold, even inhuman.
In her works Susan Haack does a marvellous job of restoring the humanity of scientists by arguing that their methods and thought processes are the same as those used by careful thinkers in any discipline. In short, she will argue that no readers should feel left behind in the preceding discussion. In a recent work, she seeks to defend science against a variety of extreme charges
In fact, I will rely upon Susan Haack's work in my claim that a science of evidence excludes no one interested in honest inquiry, a respect for evidence, and a search for truth. As she says
The core standards of good evidence and well-conducted inquiry are not internal to the sciences, but common to empirical inquiry of every kind. … respect for evidence, care in weighing it, and persistence in seeking it out, so far from being exclusively scientific desiderata, are the standards by which we judgeall
inquirers, detectives, historians, investigative journalists, etc., as well as scientists. In short, the sciences are not epistemologically privileged.
In my account of the science of evidence as a study of the properties, uses, and discovery of evidence I will claim that it includes everyone having the characteristics Susan Haack has just described. Following is just one example of persons who come to mind.
Dr. M. A. Katritzky would almost certainly not claim to be a scientist. Her interests concern historical studies in an area calledtheatre iconography
, an interdisciplinary field that involves study of events and materials associated with theatrical performances. I was first made aware of her work while writing an overview of eight studies included in a work by Twining and Hampsher-Monk
I have one final comment to make before I construct my case for a science of evidence and it concernspseudoscience
. There are many recent books and articles on the efforts of possibly unscrupulous persons to advertise their work as scientific when in fact this work does not merit such a label. How surprised I was recently to learn that persons like Phil Dawid, and I have been included in what was recently calledacademic
pseudoscience
. I have aways had the greatest respect for Professor Mario Bunge [Professor of Philosophy, McGill University, Montreal, Canada]. I read with great interest his work on causality in science
This approach contrasts with science, where gut feelings and wild speculations may be confided over coffee breaks but are not included in scientific discourse, whereas (genuine) probabilities are measured (directly or indirectly), and probabilistic models are checked experimentally.
This is the same argument that has been taking place between frequentist and non-frequentist probabilists and statisticians for decades, as Phil Dawid will certainly agree. Frequentists disavow the use of subjective probabilities that Bayes’ rule requires. Bunge bears the burden of showing just one instance in science that is free from human subjective judgment.
Bunge also bears the burden of showing how probabilities are to be determined in instances in which we have nothing to count, the events of concern being singular, unique, or on-of-a-kind. But Bunge does allow that studies of belief [he does not call it subjective probability] deserve scientific study. But, as he says
Such study is important; and, precisely for this reason, it belongs in experimental psychology and sociology, and it should be conducted scientifically. There is no reason to believe that that probability theory, a chapter of pure mathematics, is the ready-made (a priori) empirical theory of belief. In fact, there is reason to believe that credences are not probabilities, if only because we seldom know all the branches of any given decision tree.
But Bunge reserves a special place among academc chartalans for the very large number of distinguished scholars in law for their interest in what has been termed "the new evidence scholarship", a term coined a few years ago by Richard Lempert
I submit that probability hardly belongs in legal argument because probability measures only the likelihood of random events, not the plausibility of a piece of evidence, the veracity of a witness, or the likelihood that a court of law will produce a just verdict. Consequently, talk of probability in law is pseudoscientific.
In these assorted quotes, Bunge certainly reveals the extent of his myopia concerning probability. Of course he does not even mention works on other views of probabilistic reasoning such as those provided by J. Jonathan Cohen
I began this work by noting that a ranking example of the belittling of colleagues belongs to Lord Rutherford. However, all Rutherford said was that anyone not studying physics was in the field of stamp collecting. But here we have Mario Bunge referring to academic colleagues as "charlatans" engaged in "pseudoscience". This exceeds Lord Rutherford by a considerable margin, and so Bunge now tops my list. Bunge might consider issuing an apology to the many distinguished persons whose work he has disparaged simply because they do not agree with his own frequentistic view of probability.
4.0 ELEMENTS OF A SCIENCE OF EVIDENCE
The burden I now face concerns constructing defensible and persuasive arguments that systematic studies of evidence can appropriately be termedscientific
in nature. My arguments will concern studies of the classification, properties, uses and discovery of evidence. I can tell you now what my conclusions will be. Earlier, in Section 3.2, I mentioned that our studies of evidence seem to qualify as being "scientific" at least under the three "weaker", or less restrictive, definitions of science that are given in the OED. I repeat these definitions here:
1) Knowledge obtained by study; acquaintance with or mastery of a department of
learning.
2) A particular branch of knowledge or study; a recognized department of learning.
4) The kind of organized knowledge or intellectual activity of which various branches
of learning are examples.
I am going to argue that studies of evidence share several elements of the two stronger or more restrictive definitions of science that are provided by the OED:
3) A branch of study that deals either with a connected body of demonstrated truths
or with observed facts systematically classified and more or less comprehended by
general laws, and which includes reliable methods for the discovery of new truths in
its own domain.
5) The intellectual and practical activity encompassing those branches of study that
apply objective scientific method to the phenomena of the physical universe (the
natural sciences), and the knowledge so gained.
It is true of course that the standpoints of scientists and of the writers of dictionaries may be quite different. Persons who do identify their work with science will argue that even the three restrictive OED definitions are still vague and are incomplete in characterizing scientific activity. I will argue that evidence can be usefully categorized, that there are theories concerning the properties and uses of evidence, that mathematics can be profitably employed in both analytic and discovery-related activities, and that experiments of a certain sort can be performed in studies of the uses of evidence. These are all matters that many persons will argue are overlooked in the OED definitions of science.
4.1 Classification of Evidence
I begin my account of a science of evidence by reflecting on the thoughts about science provided by Jules Henri Poincaré [1854 - 1912], the celebrated French mathematician and physicist. Poincaré emphasized the importance of classification in all of science. As he said
Now what is science? … it is before all a classification, a manner of bringing together
facts which appearances separate, though they were bound together by some natural
and hidden kinship. Science, in other words, is a system of relations.
Years later, the philosopher of science, Rudolf Carnap [1891 - 1970] echoed Poincaré's emphasis on the importance of classification in science
Poincaré went on to say that the most interesting facts arerecurrent
and can be used several times. He says further that we are fortunate to be born in a world where there are such facts
4.1.1 Forms of Evidence. In my studies of evidence I have given a fair amount of thought to the manner in which evidence might be usefully classified. This would be an utterly impossible task if we just considered the substance or content of evidence. The variations in the content of evidence would be at least as great as the number of possible pebbles we could examine if we
supposed, as did Poincaré, that there were eighty million chemical elements having equal frequency of occurrence.
It seems safe to say that the substance or content of evidence is unlimited in its variety. If all evidence items are unique with respect to their content, how are we ever to say anything general about evidence? Being able to say general things about evidence is useful for many purposes, among which are thecomparative
purposes that Carnap mentioned. For example, there are at least three disciplines that come to mind in which persons drawing inference from evidence must be prepared to evaluate evidence having every conceivable substance; the fields are: law, history, and intelligence analysis. You may be able to add other fields to this list. In such instances, how are persons ever able to compare substantively different items of evidence they encounter in terms of their relevance, credibility and inferential force? Also impossible would be comparisons of evidence encountered across inference problems, perhaps in different substantive areas.
It occurred to me that evidence might be usefully classified oninferential grounds
rather than upon any grounds relying on its substance or content. What I was looking for were relations among evidence items that, as Poincaré said: "are bound together by some natural and hidden kinship". The forms and combinations of evidence I will describe are recurrent, as Poincaré also required in science; in fact, they occur in various combinations in every substantive area known to me. Figure 1 is a classification of individual items of evidence based on two inferential grounds: relevance and credibility.
In several works I have described the taxonomy in Figure 1 as asubstance-blind
classification of individual items of evidence
How do you stand in relation to this evidence item?
Generally, how does this evidence item stand in relation to what you are trying to prove or disprove?
I will show how answers to the first question involvecredibility-related
matters that serve to identify the forms of evidence listed in the rows of Figure 1. Answers to the second question involve common descriptions that refer to basicrelevance
characteristics of evidence and identify the columns in this figure.
First consider the rows in Figure 1. Different forms of evidence arise when we consider the questions you ask concerning the extent to which you might believe the event(s) recorded in the evidence. These are credibility-related questions about which I will have more to say in Section 4.2 on the basic properties of evidence. Different forms of evidence require different credibility-related questions. Some forms of evidence aretangible
in the sense that you have a direct sensory interface with evidence that may or may not reveal the occurrence of events of interest to you. The first row in Figure 1 lists a variety of common items of tangible evidence that are open to your own inspection and allow you to observe what events the evidence reveals. The plus and minus signs associated with tangible evidence refer topositive evidence
, that which reveals the occurrence of an event of interest, or tonegative evidence
, revealing the non-occurrence of an event of interest. Questions asked of the credibility of tangible evidence concern itsauthenticity
,reliability
andaccuracy
. Briefly, authenticity questions ask whether the tangible item is what it is represented to be. Reliability questions concern the repeatability or consistency of the process used in producing the tangible item. And accuracy questions concern the quality of the process by which the tangible item was produced.
In so many other cases, however, you have no access to tangible evidence you can examine for yourself in order to observe whether it reveals some event of interest to you. But you can ask another person whether or not this event occurred. In some cases, of course, this person may voluntarily tell you about certain events without your inquiring whether the events have occurred. What this other person reports to you is calledtestimonial
evidence. There are several important distinctions we have to make regarding the various forms testimonial evidence can take; the first of which occurs in the second row of Figure 1. In some cases a human source of evidence may provideunequivocal testimony
that a certain event E has occurred. This source does not hedge his/her testimony about the occurrence of this event; he/she says it definitely occurred. This would be positive testimonial evidence. But the source might instead report unequivocally that event E did not occur; this would be negative testimonial evidence.
In either the positive or negative cases of unequivocal testimony, we now encounter the array of epistemological issues I mentioned earlier in Section 3.1. Suppose a person P reports to you unequivocally that event E occurred. A natural question you could ask person P is: How do you know that this event occurred"? It seems that P has three basic responses he/she could make. They are as follows:
P says: "I observed event E myself". Let us call this a case ofdirect observation
.
Instead, P says: "Person Q told me that event E occurred". In this case we have instances ofsecond hand
orhearsay
evidence.
Or, P might say: "I had information that events C and D occurred from which I inferred that event E occurred". We can refer to this testimony asopinion
evidence.
First consider testimony based on direct observation. You have two basic questions to ask about person P; the first concerns hiscompetence
; the other concerns hiscredibility
. These are different questions and should not be confused [as they so often are]. The competence question you would ask of P comes in two parts: (i) Was P in a position where he could have observed event E, or otherwise had access to the event he reports?; and, (ii) Did P have any understanding concerning the reported event? So, access and understanding are matters concerning the competence of a source providing testimony based on direct observations.
But person P might have all the access and understanding in the world and so you
believe P to be competent. But whether you shouldbelieve
what P tells you is another matter. This raises questions about P'scredibility
. I will argue in Section 4.2 that the credibility of human sources of evidence involves consideration of a source'sveracity
,objectivity
, andobservational sensitivity
[including the conditions of observation]. These attributes come from a particular epistemological theory that has been around for a long time but is the subject of controversy. This theory is called thestandard analysis of knowledge
. Though this analysis is the subject of controversy, I have found it to be a valuable heuristic in thinking about the credibility of human sources of evidence. I will be able to back my use of this analysis by drawing upon centuries of experience in law, work in sensory psychophysics in psychology, and common experience.
Now consider second hand or hearsay evidence from source P. Person P tells you that he found out about the occurrence of event E from person Q. You may or may not be told how Q found out about event E. Perhaps Q heard about event E from yet another human source R. So we have hearsay chains of any length, some links of which can involve tangible evidence. For example, P tells you that he heard about event E from Q who says he saw a document containing a testimonial assertion by R who claims to have observed event E. In this case we have the veracity, objectivity and observational sensitivity of persons P, Q and R to worry about in addition to the authenticity of the document mentioned by Q. In another place I have examined credibility issues in hearsay chains that quickly become of baroque complexity
We might ordinarily associate hearsay evidence only with trials at law in which there are many rules restricting its admissibility. However, second hand or hearsay evidence is so common in inferences we make every day. In many cases we are not even told about who the sources are in a hearsay chain. In such instances a report is no better than rumour or gossip. How many times have you heard a news reporter say things like: "NBC has learned today that…"; or "BBC has leaned from a usually reliable source that…"? Hearsay evidence is also not uncommon in many disciplines including history, but its hazards are well recognized. The historian Marc Bloch noted that the historian relying upon hearsay evidence: "…is as if at the rear of a column, in which news travels from the head back through the ranks. It is not a good vantage point from which to gather correct information"
In the case of opinion evidence from P we have his credibility to consider as far as his alleged acquisition of information about events C and D are concerned. But we must also examine the arguments P offers to justify his conclusion that event E follows from events C and D. What we have in the case of opinion evidence resembles the testimony of expert witnesses in trials at law. Such testimony is usually contrasted with the testimony pf ordinary or lay witnesses who are required to speak from personal knowledge, as in the testimony I mentioned based on a direct observation. In many cases a person will testify about an event that may occur in the future. Such testimony can only be opinion evidence since no direct observations are possible about events that have not yet happened.
Human sources of evidence do not always state with certainty that some event of interest has occurred; they equivocate or hedge their testimony in various ways as I indicate in the third row of Figure 1. I cannot help noting that so many government, industrial and military witnesses, who appear at hearings in Washington DC, have raised testimonial equivocation to the level of an art form. This is especially true of what I have termedcomplete equivocation
. Asked whether event E has occurred, common responses are: (i) "I don’t remember"; (ii) "I don't know", or (iii) "I'm not your best witness in this matter". Unfortunately, two inferences are possible from such complete equivocation: (i) The witness is honestly impeaching his own credibility; he does not remember, he does not know, or he is not a suitable witness in the matter at issue; or, (ii) The witness does remember that event E occurred, knows that E occurred, or is a competent witness, but refuses to tell us. In instances such as in case (ii), we seem entitled to conclude that this person believes that testifying about event E would not be in his/her best interests.
Equivocation may not be complete but only probabilistic on occasion. In some cases a human source will equivocate using numbers such as: "I am 60% sure that event E occurred, and 40%
sure that it did not occur". In other cases, a human source equivocates verbally, using such statements as: "I am fairly sure that event E occurred", or: "It is very unlikely that E occurred". In such instances we might construe these probabilistically hedged responses to be indications of the source's own assessments of his/her credibility. Whether we should believe these assessments rests on other information we have about this source.
The fourth row in Figure 1 lists tangible or testimonial evidence items that we say are missing. To say that evidence is missing means that we have expected to be able to gather it but are unable to do so. In some cases our failure to obtain expected evidence can have inferential force depending on various reasons why it is missing. As we have all heard, missing evidence is not the same as negative evidence; the absence of evidence is not the same as evidence of absence. First, take the case of expected but missing tangible evidence. Perhaps you are looking in the wrong place for it; it may have been lost or destroyed; or it never existed in the first place [your expectation was incorrect]. But another explanation is that someone is withholding this evidence from you. If someone refuses to produce tangible evidence when you request it, you are entitled to draw the adverse inference that the production of this evidence would not be in the best interests of the person who refuses to produce it. This adverse inference is licensed in our Anglo-American system of law.
Refusal to give testimony is not the same as complete equivocation as described above.
In such cases a source, whom we believe to be competent, when asked whether or not event E occurred, does not even say he does not remember or does not know whether event E occurred; he says nothing. In cases at law a defendant's refusal to testify is a privilege guaranteed in our legal system, and no adverse inference is permitted from his refusal to testify. Whether this same privilege is also granted to witnesses who are not defendants is the subject of controversy. In other contexts it seems natural to suppose that a human source who refuses to tell you whether some event E happened has reasons for doing so. Inferences about what these reasons might be can be inferentially valuable.
The final row in Figure 1 contains evidence of the sort that John Locke said "rises to near certainty"
One final comment is necessary about the forms of evidence shown in the rows of Figure 1; they can occur in various mixtures that give rise to some very difficult credibility assessments. Earlier I gave one example of how we may have a mixture of testimonial and tangible evidence items in the case of hearsay evidence. But there are many other situations in which we encounter chains of various forms of evidence. Historians, for example, certainly encounter various tangible document chains or trails leading back to an alleged testimonial assertion made by some historically interesting person. Your passport supplies another example of a document trail leading back to a birth certificate on which is recorded the time and place of your birth as witnessed by the obstetrician or other person who assisted in bringing you into the world.
Now consider the three columns in Figure 1 that involve terms commonly associated with some very general relevance relations. As I noted, these terms arise in response to your question: how does this evidence stand in relation to what I am trying to prove or disprove? The first distinction I have made is betweendirectly
andindirectly relevan
t evidence. This distinction is necessary since we have evidence and evidence about this evidence. Evidence is said to bedirectly relevant
if you can link it by a defensible chain of reasoning to hypotheses you are considering. Even if you cannot establish this linkage, evidence can still be relevant, but only indirectly so, if it bears upon the strength or weakness of directly relevant evidence. It is common to refer to this evidence as beingancillary evidence,
since it is evidence about other evidence. Wigmore understood the distinction between directly relevant and ancillary evidence as did another prominent scholar of evidence. As the Swedish jurist Per Olof Ekelof noted: "What we call a 'piece of evidence' is strictly speaking an evidentiary fact together with auxiliary facts attached to it"
I have listed two forms of directly relevant evidence:direct
andcircumstantia
l evidence. Direct evidence, if credible, is said to go in one inferential step to a matter revealed in the evidence. In other words, credible direct evidence is conclusive on a matter revealed in the evidence. Circumstantial evidence, on the other hand, is always inconclusive on some matter, even if it is perfectly credible. I have preserved the distinction between direct and circumstantial evidence in Figure 1 on the off chance that you seen these two terms used on occasion. However, in our recent work on evidence we have dropped this distinction
In summary, Figure 1 shows fifteen generic and recurrent forms of individual items of evidence. This number is reduced to ten if we drop the distinction between direct and circumstantial evidence. Recall that mixtures of these forms of evidence are possible in any context or situation, as I illustrated. The example I gave involved cases in which we have testimonial evidence contained in a tangible document.
4.1.2 Combinations of Evidence. I have gone one step further in my evidence taxonomy by considering various generic and recurrentcombinations
of two or more evidence items. In another work I have provided diagrammatic representations of these combinations and more extensive discussions of them
Two or more items of evidence can beharmonious
in two basic ways. The evidence can becorroborative
when two or more sources [of whatever kind] report or reveal the same event. For example, two human witnesses and a photograph, all tell us that event E occurred. But harmonious evidence can also beconvergent
in the following way. We have evidence from two or more sources aboutdifferent
events, all of which favour the same conclusion. As an example we have evidence about events E and F where we believe that both of these events favour proposition or hypothesis H. Evidence combinations reveal many interesting and important subtleties or complexities that can be exploited if they are recognized. A very important subtlety associated with convergent evidence is their possiblesynergism
: two or more convergent items of evidence can have increased inferential force when they are considered together than they would have if they are considered separately or independently. As an example, we continue to believe that evidence about events E and F, if credible, would each individually favour H. But we also believe that, taken together, they interact inferentially in favouring H to a greater extent that they would do if we did not notice their synergistic effect when they are considered together.
Failure to recognize convergent evidential synergism can be inferentially hazardous as we witnessed following the September 11, 2001 terrorist incidents in New York City and Washington, DC. Our FBI and CIA each had evidence pointing toward immanent terrorist activities but such evidence was never considered jointly. In part this was due to statuary restrictions on the sharing of information between these two agencies. Had items of in formation been shared by these two agencies at least the attacks on the World Trade Center in New York, using airliners as weapons, could have been anticipated and perhaps avoided. Evidential synergisms cannot be recognized and exploited when information is not shared.
Two or more items of evidence can bedissonant
in two basic ways that are often confused. Evidence iscontradictory
if it reports the existence of mutually exclusive events, those which cannot happen together. In the simplest of cases, one source reports to us that event E occurred [this would be positive evidence of E as noted in Figure 1] But another source tells us that event E did not occur [this would be negative evidence of E]. A contradiction would not necessarily involve evidence about binary events such as E and not-E. For example, one source tells us that Osama Bin Laden was in Kabul, Afghanistan on the morning of March 4, 2003; but another source tells us that he was in Karachi, Pakistan at this same time. Osama cannot have been at both of these places at the same time.
However, Kabul and Karachi clearly do not exhaust all the places where Osama might have been at this time.
But another form of dissonant evidence isdivergent
in character.
Here we have evidence about two events that can happen together but simply point us in different inferential directions. A contradiction always involves events that cannot happen together. I once was asked to analyze evidence obtained from over 50,000 patients who had experienced cardiothoracic surgery.
Many of these patients lived, but some died. Two of the many indicators that were gathered from those who lived and those who died were: (i) the patient's age at the time of surgery, and (ii) the number of previous episodes of cardiothoracic surgery the patient had experienced. As you might expect, the younger a patient is the better are the chances of surviving this kind of surgery. But the existence of prior episodes of cardiothoracic surgery reduce the chances of this person's surviving another episode of this kind of surgery. Now, here comes a patient who is young; he is just twenty years old. This seems to favour his surviving the heart surgery that is being considered in his case. But we also observe that he has had prior heart surgery several years ago. This seems to disfavour his survival from the contemplated heart surgery. Notice that these two events can happen together; they are divergent in their inferential implications but are not mutually exclusive events.
Resolving evidential contradictions rests upon credibility issues. Since the events in contradictory evidence cannot occur jointly, one or the other of the sources must have been untruthful, not objective, or mistaken. But resolving evidential divergence is a more complex matter. Credibility issues arise, but there are other things to consider. In some cases it may be said that we lack understanding of what the evidence is telling us and we may be mistaken in saying that the evidence diverges. In some situations we can resolve evidential divergence by considering the joint occurrence of the events reported. We encounter no logical difficulties here because the events reported in such evidence can occur simultaneously, as I illustrated in my cardiothoracic surgery example. We can have a patient who is young but who also has had prior episodes of this surgery. When we examine the joint occurrence of these two events, we find that prior episodes of cardiothoracic surgery actuarially swamp patient age and so the divergence disappears. Our initially saying the age and prior episodes of surgery are divergent was based on treating these two diagnostic indicators separately or independently.
Finally, two or more evidence items can beinferentially redundant
in one of two basic ways. In such instances the inferential force of one item of evidence can be reduced when other evidence is considered. The first pattern of redundance is said to becorroborative
in nature. When we hear about thesame event
from several different sources [as in the corroborative case of harmonious evidence mentioned above], successive accounts of this same event usually mean less to us. All depends on the credibility of our sources of information about this event. If we believed our first source of evidence about this event was perfectly credible, then additional accounts of this same event would be completely redundant and would add no inferential force since they tell us something we already believe. The second account of this event springs to life to the extent that we find the first source not credible. The third account of this event springs to life to the extent to which we believe the second source not to be credible, and so on.
But there is a pattern of redundance that can involve evidence ofdifferent events
; I have called this patterncumulative redundance
. I have chosen the word "cumulative" that is used in the field of law to indicate evidence that adds nothing new. Suppose source P reports that event E occurred and source Q reports that event F occurred. We believe that if event E occurred this would reduce the force of knowing that F occurred. Here is an example that comes from the analysis Jay Kadane and I performed on the evidence in the celebrated American law case involving Nicola Sacco and Bartolomeo Vanzetti
The prosecution produced two witness whom the press labelled "star" witnesses. The first was a man named Lewis Pelser; the second was a man named Lewis Wade. Pelser testified that he saw Sacco at the scene of the crime at the time it was committed. The prosecutor expected Wade to corroborate Pelser's testimony by saying that he also saw Sacco at the scene of the crime when it was committed. But this is not what Wade testified; he only said that he saw someone who looked like Sacco at the scene of the crime when it was committed. Thus, Pelser and Wade reported different events; Sacco's being there and someone looking like Sacco being there are not the same events. In any analysis of the testimony from these two witnesses credibility plays the same crucial role as it does in the case of corroborative redundance. If we believed Pelser to be perfectly credible, then Wade's testimony tells us nothing, since if Sacco were indeed at the scene and time of the crime, then someone who looked like Sacco was certainly there. But Wade's testimony springs to inferential life to the extent that we believe Pelser was not credible in his testimony.
There was a variety of evidence introduced that undermined Pelser's credibility and a smaller amount that undermined Wade's credibility. Unfortunately, this unfavourable evidence had little if any effect on the twelve jurymen who voted for the conviction of Sacco and Vanzetti.
4.1.3 On "Substance-Blindness". I have now completed a description of my categorization of recurrent forms and combinations of evidence. There are two reasons why I have dwelt on this matter; the first concerns the importance both Poincaré and Carnap placed on classification in science. No science of evidence would be possible if we could not classify evidence in any meaningful way. I understand that there are various ways in which evidence might be classified. I will put my classification of forms and combinations of evidence to use in Section 4.3.1.
The second reason for my dwelling upon classification involves my use of the term "substance-blind" with reference to the evidence classification I have proposed
I'll close my account of subtance-blind evidence classification with two sets of examples that I hope will illustrate what Poincaré said about "…facts which appearances separate, but which are bound together by some natural and hidden kinship". The first involves tangible evidence. You would be hard-pressed to find a greater substantive disparity between the kinds of evidence Dr. Katritzky encounters in her studies of theatre iconography in past ages and the kinds of ballistics evidence encountered in a murder trial. If you look at her Plate 3 on page 240 of her work that I have cited
Now consider the murder trial of Sacco and Vanzetti
We have tangible objects in both of these situations; a drawing and a bullet. What is their "natural and hidden kinship"? This kinship come in the form of the identical credibility issues they both raise. The first is Dr. Katritzky's concern about theauthenticity
of the figure in her Plate 3. Was it really compiled, and perhaps drawn, by M. A. Pribil sometime during the years 1587 - 1594? Howaccurate
was this drawing as a representation of mountebanks' costumes? Did M. A. Pribil actually attend the mountebank performance in which the characters were wearing the costumes depicted in the figure? How good an artist was Pribil? Sadly, her devoted concern about authenticity was nowhere evident concerning Bullet III in the Sacco and Vanzetti trial. No one asked the question: Was Exhibit 18, shown at trial, the same Bullet III that Dr. Magrath extracted from Berardelli's body? Both the prosecution and the defence were allowed to test-fire bullets through Sacco's Colt automatic. One distinct possibility, much discussed, is that the prosecution substituted one of the bullets test-fired through Sacco's weapon for the real Bullet III that had been extracted from the guard's body. In short, the Bullet III shown as Exhibit 18, may not have been authentic.
There was concern, exhibited by the defence, about the accuracy, and perhaps reliability, of records concerning the chain of custody through which Exhibit 18 might have passed. There were many missing or weak links in this chain of custody that have been recognized by all commentators on this case, but they obviously had little if any impact on the jurors who tried the case.
My examples of testimonial evidence come from two disparate situations; a psychoanalytic interview and a terrorist investigation. In a psychoanalytic session patients naturally give testimonial accounts of their difficulties and their experiences. In the investigation of a terrorist incident reliance is placed on HUMINT [human intelligence] that often comes in the form of a person's report about what he/she has seen or heard. What is the "natural and hidden kinship" among these two contexts in which people give testimonial evidence? The answer is the concern in both situations about attributes of thecompetence
andcredibility
of the persons who provide testimony. As I noted above in my discussion testimonial evidence in Figure 1, attributes of competence involve access to the information reported as well as understanding of it. Credibility attributes involve the veracity, objectivity and observational sensitivity or accuracy of person providing testimony.
There is concern in the field of psychoanalysis about the credibility of patient reports of their difficulties and the experiences they encounter
4.2 Studies of the Properties of Evidence.
I have just shown how recurrent forms and combinations of evidence can be classified in what I regard as useful ways, regardless of the substance or content of the evidence. But there is so much more to a study of evidence than just identifying what types of evidence we may encounter in any situation. Evidence has several important inferential properties that I have referred to on occasion as "credentials". These properties, which I will now consider, are:relevance
,credibility
andinferential [or probative] force. weight or strength
. A fourth property may be identified,completeness
orsufficiency
, but I will include this property in my discussion of inferential force, weight or strength. The reason is that one view of the weight of evidence rests upon the degree of its completeness.
My objective in this section is to continue to show how studies of evidence involve the three major concepts Carnap identified as being associated with science: classificatory, comparative, and quantitative
I note that these properties or credentials of evidence immediately raise matters that do depend upon the substance or content of evidence and the particular context or situation in which the evidence is being employed. In short, these credentials arenot "substance-blind"
. The major reason is that evidence never comes to us with these credentials attached; they must be established by defensible arguments that rest upon the substance or content of the evidence as well as the nature of its linkage to the propositions or hypotheses at issue in the evidence-based inference task of concern in a particular context or situation.
Finally, I note that theories abound in all of the sciences as well as in many other contexts. In fact, a compilation of over five thousand theories occurring in a wide variety of disciplines is available
4.2.1 On the Relevance of Evidence
At the most general levelrelevance
answers the question: So what? You receive an item of information or a datum and ask how this information bears upon anything of interest to you. Charles Darwin once asserted that any observation must be for or against some view if it
is to be of any service at all
As I noted in discussing Figure 1, a distinction must be made between directly relevant and indirectly relevant [ancillary] evidence. Here I introduce several terms I have borrowed from Wigmore
Now, the "glue" that either holds, or fails to hold, our relevance arguments together consists of generalizations, that license reasoning from one probandum to another, together with ancillary evidence that either supports or undermines the applicability of a generalization in the particular case in which it is being applied. Thus, the applicability of a generalization rests upon the quality and completeness of ancillary evidence. I note here that Toulmin, discussing the ingredients of argument from evidence, has used the termwarrant
orlicense
instead of the termgeneralization
; and he used the termbacking evidence
instead of the termancillary evidence
Generalizations, warrants or assumptions are necessary ingredients for establishing the relevance of evidence. In an argument concerning relevance, particularly one having many links or inferential steps, generalizations are frequently not overtly expressed but often lurk in the background. Though they are necessary in all arguments from evidence, there are some distinct hazards associated with them. In addition, many kinds of generalizations have been identified along with various inferential hazards they present
Before I consider various theories concerning relevance, I must briefly mention two basic forms of argument structures that arise in complex inferences based on a mass of evidence. These structures have a name currently given to them; they are calledinference networks
. The first person known to me to provide a systematic study of complex inference networks was Wigmore
An example of a Wigmore evidence chart appears below in Figure 2A. Wigmore argument structures tend to be hierarchical in nature with lines of inductive inference proceeding from the evidence to an ultimate probandum. The interim probanda in such argument structure represent sources of doubt that may be interposed between evidence and penultimate probanda. So, an inference network in a Wigmore chart has lines of reasoning, indicated by the arrows, go from the evidence to an ultimate probandum. Thus, the arrows or links in such a chart indicate avenues by which items of evidence are relevant on a penultimate probandum. Wigmore's basic use of an inference network was to chart stages of argument in the task of trying to draw conclusions from an emerging mass of evidence.
Constructing an argument in defence of the relevance of a single item of evidence is often a difficult task. But constructing relevance arguments from an entire mass of evidence, by means of a Wigmore inference network, can be an astonishing difficult task. I know this from first-hand experience. Jay Kadane and I constructed an inference network based on 395 items of trial and post-trial evidence in the Sacco and Vanzetti case
But not all inference networks have the hierarchical structure of a Wigmore network. An example of a network having a different structure appears in Figure 2B. In another work I have called such networksprocess models
in which the objective is to analyse a complex process consisting of variables believed to be involved in this process are linked together in certain ways
As I noted earlier, mathematics enters our studies of evidence when we examine the structure of arguments we generate from evidence. The mathematical theory of graphs forms an underpinning for the argument structures we generate. The two forms of argument construction just shown in Figure 2 have a different structural appearance but they have a common property. They are both examples of what are calleddirected acyclic graphs
[DAGs]. The termdirected
means that there are lines of inference showing relevance, probabilistic influence, or perhaps causal influences among the elements [probanda or variables] in the structure. These are indicated by the arrows. The termacyclic
means that you cannot follow a chain of linkages or arrows that leads you right back to where you started. This would be a most unfortunate property for an evidence-based argument to have. Imagine an argument that leads you right back to where you started. You would be in an inferential loop and you would never be able to draw any conclusion or generate any meaningful relevance argument. I have found it interesting to note that the arguments Wigmore generated in 1913 had this DAG property well in advance of developments in the mathematics of graph structures.
I now consider two theories concerning relevance. In the first, relevance is not a matter of degree, but in the second it is. I will first consider relevance as it is viewed in the field of law. In America, the Federal Rules of Evidence provide a definition of relevance by means of Federal Rule of Evidence [FRE] 401
"Relevant evidence" means evidence having any tendency to make the existence of any fact that is of consequence to the determination of the action more probable or less probable that it would be without the evidence.
In the Advisory Committee's Notes to FRE 401, several interesting comments are provided regarding this definition. They first note that relevance is not an inherent property of evidence but exists only as arelation
between an item of evidence and a matter properly provable in the case. This relation obviously must be in the form of a defensible or logically sound argument linking the evidence with the matter to be proved [aprobandum
, to use Wigmore's term]. I can't help recalling Poincaré's assertion that science is a system of relations
Another important matter addressed in the Advisory Committee's Notes to FRE 401 concerns the following consequence of the definition given in this rule. Notice that FRE 401 does not say how much more probable or less probable relevant evidence should make the existence of any fact that is of consequence to [or is material to] the action. The Advisory Committee noted that any more stringent requirement than "more probable or less probable" would be unworkable and unrealistic. All FRE 401 says essentially is that relevant evidence must havesome
probative or inferential weight, force or strength in changing our beliefs about this material fact. So, there is a direct connection between relevance and probative or inferential force. As I will discuss further in Section 4.2.3, we can grade probative or inferential force in various numerical ways, but a similar grading of relevance is not possible. I also noted how Richard Lempert saw the connection between relevance [as given in FRE 401] and probative force
It is true that relevance, as it is defined in FRE 401, is not a matter of degree. However, in some cases we may require evidence of another matter F to justify the relevance of evidence E. Federal Rule of
Evidence 104b covers
such
situations
When the relevancy of evidence depends upon fulfilment of a condition of fact, the court shall admit it upon, or subject to, the introduction of evidence sufficient to support a finding of the fulfilment of the condition.
The basic problem addressed by FRE 104(b) is that evidence is presented seriatim at trial and not all in one lump. Defence of the relevance of evidence E might have to await the presentation of evidence F. But this does not say that evidence E has any particular degree of relevance, even if condition F is satisfied.
I now consider a very interesting alternative view of the concept of relevance proposed by Dan Sperber and Deirdre Wilson
In Sperber and Wilson's view relevance is a matter of degree
Byassumptions
, we mean the thoughts treated by an individual as representations of the actual world (as opposed to fictions, desires, or representations of representations).
As I read this, it seemed to me that their use of the termassumption
is closely related to what I mentioned earlier asgeneralizations
. I had said that generalizations and ancillary evidence form the "glue" that holds, or fails to hold, our arguments together. An obvious way of criticizing an argument is to examine whether the underlying generalizations or assumptions, and their evidential backing, seem to make sense. In extreme cases we would have a non sequitur in which one proposition in a chain of reasoning does not follow from a preceding proposition. But the links in chains of reasoning in an argument will vary in strength depending upon a number of factors involving the strength with which we believe an asserted generalization or assumption holds as well as the number of links in the chain of reasoning.
I short, some arguments seem stronger than others, this is just one example of how Carnap'scomparative
concept enters our discussion of relevance. The glue holding together some arguments is stronger then the glue holding together others. In the case of a non sequitur we might assert that the wrong glue is being used. Sperber and Wilson allow that assumptions can vary in their strength
I now relate assumptions to Sperber and Wilson's view of the manner in which there are degrees of relevance. I will first note that an assumption or generalization, being someone's assertion of how the actual world works, always depends on context. One way of showing that an asserted assumption or generalization holds in the situation in which it is asserted is to back it with appropriate ancillary evidence. What the authors do in showing that relevance is a matter of degree, is to subject the assumptions/generalizations we make to what they call a cost/benefit analysis in terms of the effect and effort related to the assumption/generalization. Here is what they have said about the extent of relevance and its dependence upon the effect and effort of assumptions
Relevance:
Extent Condition
1: an assumption is relevant in a context to the extent that its contextual effects in this context are large.Extent Condition
2: an assumption is relevant in a context to the extent that the effort required to process it in this context is small.
It seems thatExtent Condition
1 refers to the strength with which we can back up an asserted assumption/generalization in which we have expressed great confidence. In other words, we believe the glue holding together this particular step in our argument is very strong. ButExtent Condition
2 also requires that we can easily show how the backing evidence we have does support the assumption/generalization we have asserted. In so many cases we would all be quite at home arguing about the extent to which we have appropriately backed an asserted assumption/generalization.
I close my discussion with an example I hope will show the relationship between the two views of relevance I have mentioned. There is nothing about the Sperber and Wilson view that argues against the view of relevance as expressed in the field of law. Recall that FRE 401 simply says that evidence is relevant only if it hassome
force in changing one's belief about the probability of an event of consequence in a trial. The example I have in mind comes from an argument I constructed in our analysis of the evidence in the case of Sacco and Vanzetti. At this trial a prosecution witness, a police officer, named Michael Connolly, testified that he had tried, without success, to keep Sacco from putting his hands under his coat. Sacco had acknowledged that he was carrying an automatic pistol at the time of his arrest, but he specifically denied what Connolly said in his testimony. The judge ruled that Officer Connolly's testimony was relevant and it was admitted. The judge later told the jurors that Connolly's evidence was very powerful because it showed Sacco's consciousness of having killed the payroll guard.
But at trial the prosecutor, Frederick Katzman, was never asked to produce an argument showing exactly how Connolly's evidence was relevant in an argument that Sacco knew he had committed the crime with which he was charged. But in our analysis of this case I was obliged to try to construct an argument in defence of Connolly's testimony. My argument or chain of reasoning consisted of eight links which I have described showing the generalizations I was obliged to assert at each link in this argument
The events reported by police officers testifying under oath usually have occurred.
Persons who intend to intend to use or threaten to use weapons on arresting officers will most often do so because of their intention to escape from custody.
Persons who intend to escape from arresting police officers are usually conscious of having committed a criminal act.
The evidence backing the first generalization was not favourable to it; Connolly may have "cooked up" this story. There was no evidence at all to back up the second generalization. There was evidence bearing on the third generalization, but it acts to diminish its effect [to use Sperber and Wilson's term]. Sacco said he was conscious of having distributed seditious literature which was, at the time, against the law. The long and short of it is that I managed to construct an argument in defence of an item of evidence that I believe has the same degree of strength as the soup that Abraham Lincoln once described that was "made by boiling the shadow of a pigeon that had already been starved to death". The analysis by Sperber and Wilson is valuable in showing how the inferential force of evidence, which can be graded in various numerical ways, depends on the generalizations/assumptions we assert. But they do not suggest that we can grade the relevance of evidence in any numerical way. No Federal Rule of Evidence makes this suggestion either. The overall cogency or defensibility of an argument, and the generalizations/assumptions on which it is grounded, cannot be cast in numerical terms.
4.2.2 On the Credibility of Evidence and Its Sources.
Given an item of information in the form of a tangible object or a testimonial assertion, the question is: can you believe what this item says? You may of course have asked this question before you asked the "so what?' question concerning the relevance of this item. In any case, as I noted in my discussion of Figure 1, the credibility questions you ask of tangible evidence are different from the ones you ask of testimonial evidence provided by human sources. But I also noted that we can have mixtures of tangible and testimonial evidence where we have both kinds of questions to answer, such as instances in which we have a tangible document recording the testimony of a human source.
In Section 3.1 I mentioned the epistemological issues we naturally encounter in assessing the credibility or believability of evidence. It is now time for me to consider these issues in more detail. As I proceed, I will continue to focus on matters that will arise in any discussion about there being a science of evidence.
I first need to mention the role of credibility questions in the construction of arguments based on evidence. Credibility questions always form the very foundation of any arguments we generate concerning the relevance of evidence [of any kind]. A very simple example is shown in the chain of reasoning in Figure 3.
Suppose we have evidence E* that event E occurred. We must always distinguish between evidence for an event and the event itself. Thus evidence E*, that event E occurred, is not the same as the actual occurrence of event E. For the moment forget about whether E* is tangible or testimonial evidence. Suppose we all agree on the suitability of the generalizations/assumptions that license steps in our relevance argument on a probandum of interest: is proposition or hypothesis H true? Here is our relevance argument: "The occurrence of E licenses an inference of F; F licenses an inference of a G; and, in turn, G licenses an inference of H. Our generalizations licensing this chain of reasoning are all appropriately hedged. We are not asserting that E makes F necessary, F makes G necessary, or that G makes H necessary. What we have in this relevance argument are three sources of doubt.
But the very foundation for this argument comes in the form of the inference we must make about whether or not event E occurred based on evidence E*. Just because we have evidence E* does not entail that E did occur. Based on E* we must first make an inference about the extent to which we can infer that event E did occur. This is the credibility-related foundation stage of the entire argument shown in Figure 3. So, there are four sources of doubt interposed between our evidence E* and the proposition H we are trying to prove from it. These sources of doubt are indicated by the questions shown in Figure 3.
I know of no branch of science, or any other area of serious investigation, in which credibility-related matters are ignored. The chemist or physicist is every bit as concerned about the credibility of what their instruments tell them as the psychologist is in the credibility of various forms of evidence they collect about elements of human behavior. I have already noted the care that Dr. Katritzky has taken concerning the credibility of the evidence she gathers in her studies of theatre iconography. So, a science of evidence must be able to say useful things about the credibility of any kind of evidence encountered in any situation. In my remarks on credibility I will make use of all three of Carnap's concepts in science: classificatory, comparative, and quantitative. In Figure 1 I have already made use of a classificatory concept by distinguishing among the various forms of evidence by means of the credibility-related questions they impose.
Before I dwell further on the attributes of tangible and testimonial forms of evidence, I need to make additional comments about the chain of reasoning shown in Figure 3 that combines relevance stages and a credibility-related foundation stage. A simple truth is that the relevance or credibility stages of any chain of reasoning we might generate can always be decomposed to reveal additional sources of doubt. For example, suppose a critic arrives and examines the relevance stages of our argument as shown in Figure 3. The critic says: "I don't believe you can infer G directly from your F. You need another stage in your argument, namely interim probandum J , that can be inferred from your F, and which will allow you to more appropriately infer your G". In addition, as I will later discuss, the credibility-related foundation stage of this argument can be decomposed to reveal specific concerns about the attributes of either tangible or testimonial evidence. Our concerns about each of these credibility attributes represent additional sources of doubt. Interesting epistemological issues arise at this point. In the case of testimonial evidence I need to explain where the three attributes I have identified come from. I will make use of a theory from epistemology to identify attributes of the credibility of testimonial evidence.
0%
Author: DAVID A. SCHUM
