Alhassanain(p) Network for Heritage and Islamic Thought

Complex Ideas

Although he granted that some groups of simple ideas naturally occur together in our experience, Locke supposed that most of our complex ideas are manufactured in the human mind by the application of its higher powers. Combining joins several simple ideas together in the formation of a new whole; comparing brings two distinct ideas together without uniting them, giving rise to the idea of a relation between them; and abstracting separates some aspect of an idea from its specific circumstances in order to form a new general idea.

Repeated applications of these powers, Locke supposed, give rise to the whole variety of ideas human beings are capable of having. [Essay II xii 1-2] If we're going to analyze the epistemic origins our complex ideas, it will be helpful to consider the ways in which we gradually build up our supply of them.

On Locke's view, complex ideas are of three varieties: Modes are invariably conceived as the features of something else, which are never capable of existing independently. Substances, on the other hand, are understood to be the existing things in which modes inhere. Relations are nothing more than mental comparisons in some respect among other ideas. [Essay II xii 3-7] Complex ideas of all three sorts are manufactured by the mind from simpler components.

Modes

A simple mode is a complex idea all of whose component parts are variations or combinations of a single simple idea. [Essay II xii 4-5] Consider, for example, the simple idea of space: acquired initially from our senses of sight and touch, this idea provides the sole content for a host of related ideas of our own manufacture.

The notion of one-dimensional length can be "folded" upon itself to yield those of area in two dimensions and capacity in three; these notions, in turn, can be modified more subtly to provide our ideas of shapes and figures. Even the notion of place in relation to other bodies within a framework Locke believed to be abstracted from the simple idea of space. [Essay II xiii 2-6]

In similar fashion, Locke supposed that the simple idea of unity, repeatedly recombined with itself, provides the entire content for the simple modes of number, including even that of infinity. [Essay II xvi - xvii] In every such case, the complexity of the simple mode arises only from an iteration of a single simple idea, upon whose content the complex idea therefore relies.

Mixed modes, on the other hand, are complex ideas whose components include several distinct simple ideas, often including those derived from different experiential sources. Although such ideas can be acquired through observation of their instances in our experience, Locke supposed that they are much more commonly manufactured by the mind as complex ideas before we first apply them to the world. [Essay II xxii 1-2] This is an important feature of our complex ideas of mixed modes. Among them are included the conceptions we form of human activities, which typically involve not only ideas of sensation describing the overt action but also ideas of reflection regarding the intention with which it is undertaken.

For Action being the great business of Mankind, and the whole matter about which all Laws are conversant, it is no wonder, that the several Modes of Thinking and Motion, should be taken notice of, the Ideas of them observed, and laid up in the memory, and have Names assigned to them; without which, Laws could be but ill made, or Vice and Disorder repressed.

Nor could any Communication be well had amongst Men, without such complex Ideas, with Names to them: and therefore Men have setled Names, and supposed setled Ideas in their Minds, of modes of Actions distinguished by their Causes, Means, Objects, Ends, Instruments, Time, Place, and other circumstances; and also of their Powers fitted for those Actions. [Essay II xxii 10]

The idea of stabbing, for example, typically involves a deliberate act of penetrating flesh without any presumption about the instrument employed to do so. In such cases, it may be worthwhile for legislative bodies to conceive of such actions and condemn them as criminal without having to have experiential evidence of their first occurrence. [Essay III v 2-6] The only thing that matters for the formation of a mixed mode, on Locke's view, is the convenience of its use for us.

This clearly varies among distinct cultures, since the frequency with which we have occasion to notice, denominate, and evaluate actions of particular sorts often depends upon their social context. Invented wholly for our own use in matters of moral and legal import, the ideas of mixed modes have only that specific content we choose to give them. [Essay II xxii 5-12] As we'll see next time, the freedom with which such ideas are manufactured renders problematic our ability to use a common vocabulary in reference to them.

Relations

Complex ideas of relations derive from the mental operation of comparing distinct ideas without thereby combining them together into an entirely new whole. [Essay II xii 1, 7] Since this comparison considers each of the ideas in light of its extrinsic conformity with the other, it is commonly expressed by means of one of a pair of reciprocal relative terms-"parent"/"child" or "cause"/"effect," for example.

This is not invariably the case, however, so we must be alert to the possibility that apparently positive terms implicitly signify comparison with something else: "old" or "imperfect," for example. The tip-off to such cases, on Locke's view, is that (as in the case of relations of the other sort) removal of the correlative destroys the relation completely, rendering the term inapplicable. [Essay II xxv]

Many of our ideas of relations are acquired through sensory experience of the modes of time, place, and number. The correlative ideas of cause and effect are a special instance, on Locke's view: observing the changes produced in one thing by the operation of another, we form a sensitive notion of the causal relation even though we have no conception of the underlying mechanism at all. [Essay II xxvi 1-6]

Because language is devised for our convenience in satisfying the needs of ordinary life, things that are commonly connected in observation give rise to our complex ideas of natural relations. But we also conceive of instituted or voluntary relations between things that are corrleated with each other only by virtue of our own personal or social agreements.

Among these, on Locke's view, the most important and vital are the moral relations drawn between the complex ideas of specific human actions, together with their circumstances and goals, and the moral rules by reference to which we evaluate them. [Essay II xxviii 1-4] We'll look at these much more closely later on.

Substances

According to Locke, the complex idea of a substance is a collection of simple ideas that is believed capable of existing independently. Observing in experience that several features recur together frequently, we suppose that there must be some common subject that has all of them. Thus, for Locke, the "Notion of pure Substance in general" is nothing but the assumption of an unknown support for a group of qualities that produce simple ideas in us; our only notion of this putative "substratum" in itself is the confused notion of "that which" has these features, or "something, I know not what." [Essay II xxiii 1-3]

Locke consistently ridiculed the use of such scholastic terms as "Inhaerentia" and "Substantia" as pointlessly circular efforts to provide a positive idea of something for which, in fact, "we have no Idea of what it is, but only a confused obscure one of what it does." From this, he supposed, we can infer little of the metaphysical nature of reality. [Essay II xxiii 17-20]

Nevertheless, just as we combine simple ideas of qualities and powers to form the complex ideas of individual substances, we also gather many distinct things under the even more complex ideas of collective substances-army, world, and universe. [Essay II xxiv 1-3]

To the confused idea of substance in general, Locke held, we add either the ideas of regularly observed sets of sensory qualities, in order to form the notion of a bodily substance, or the reflective ideas of various kinds of mental operation, in order to form the notion of a spirit or thinking thing. Since the underlying nature of the substrate is equally obscure in both cases, the "secret and abstract Nature of Substance in general" is equally unknown to us for substances of either sort. [Essay II xxiii 4-6]

We do have clear and distinct ideas of the primary qualities of both bodies (solidity and impulse) and mind (thinking and motivity) even though our sensation and reflection offer no insight into "the internal Constitution, and true Nature of things," so that the relation and/or independence of bodies and minds remains an open question. [Essay II xxiii 29-32]

Thus Locke argued that even though we are often more familiar with material objects than with spirits, our ideas of them may be no clearer, and the customary prejudice in favor of bodily substance is philosophically indefensible. [Essay II xxiii 15-16]

With respect to bodily substances, the most accurate complex idea we could form, on Locke's view, would be one that includes the ideas of those active powers and passive capacities that it exhibits in its interaction with other things-the magnetism of the lodestone and the flammability of wood-along with its characteristic weight, color, or heat.

Since he believed the primary qualities of bodies to reside in the unobservable texture of their sub-microscopic parts, Locke found it natural to suppose that we classify distinct kinds of body by reference to the secondary and tertiary qualities these unknown features produce in us or other things. [Essay II xxiii 7-10] To express one of Locke's favorite examples in our own idiom, we were able to identify genuine pieces of gold for centuries before we had any clue to its atomic structure.

Representational Reliability

Several late chapters of Book II are devoted to a detailed discussion of the success with which ideas of various kinds perform their representative functions. The point here is that since we use ideas as signs, it is vital to be aware of the likelihood that they do actually point beyond themselves to their intended referential objects. The extent to which they serve these functions will determine the reliability of any knowledge we try to acquire about those objects.

Locke explained the clarity of ideas by analogy to visual perception: just as an object is seen clearly when viewed in suitable light, a clear idea is one of which we have a "full and evident perception," whose content is present before the mind. An idea is distinct, on the other hand, when it is perceived to differ from all others. [Essay II xxix 2-5]

Locke had no stake in differentiating sharply between the clarity and distinctness of ideas. In the Essay's fourth edition, he made a half-hearted effort to substitute the single adjective "determined" in place of the customary pair "clear and distinct." His central concern was with the failure of this representational function, in ideas that are confused. This occurs most frequently with respect to complex ideas, whose simple components may be too few or too poorly organized to determine their content precisely.

The problem, Locke argued, is that we often use words as if we knew their significance when, in fact, the ideas associated with them are not fully conceived. [Essay II xxix 7-11] We'll consider this issue more fully next time, but it's worth noting that Locke believed that many apparently intractable philosophical disputes arise from a failure to employ words to signify clear and distinct ideas.

His examples here all arise from the wide-spread failure to hold in mind a correctly-formed, determined idea in association with the word, "infinity." [Essay II xxix 13-16]

In Locke's taxonomy, and idea is said to be real (as opposed to fantastical) so long as there is something that it represents. Notice that the accuracy of representation is not at issue here at all. Even if the idea fails to correspond to its object, it is real provided only that the object does exist. Since simple ideas are passively received in the mind, for example, they must be caused by something real, even though-as we've already seen-in the case of secondary qualities they fail to resemble their causes. [Essay II xxx 1-2]

Because our complex ideas of modes and relations are not supposed to refer to anything else beyond their own archetypal content, they are all real as well. Ideas of substances, however, are intended to refer to existing things and are therefore fantastical if things with the appropriate combinations of features do not in fact exist. [Essay II xxx 4-5]

An idea is further said to be adequate only if it represents its intended object fully and perfectly; inadequate ideas convey the nature of their objects only partially. [Essay II xxxi 1] Locke insisted that all simple ideas are adequate, though doing so required some fancy footwork with respect to our ideas of secondary qualities. Properly understood, he argued, simple ideas represent whatever power it is that produces them in us, whether or not the idea resembles that power-which, in the case of secondary qualities, it does not.

As with the reality of ideas, so with their adequacy the vital point for Locke was the causal process by means of which we acquire them; our lack of voluntary control over that process forestalls any possibility of mistake or erroneous judgment. [Essay II xxxi 2, 12] Because complex ideas of modes and relations are assembled by the mind without reference to any external archetype, they are their own archetypes, which they cannot fail to capture adequately.

Although our communication with each other about such ideas (especially in the case of mixed modes) may falter because we do not agree about the signification of words we both employ, the ideas themselves are invariably adequate. [Essay II xxxi 3-5, 14] Once again, it is complex ideas of substances that are unreliable; such ideas, according to Locke, have a double intended reference but are inadequate in both respects.

If they are supposed to represent the substantial forms of existing things, our ideas of substances are inadequate because (on the corpuscularian theory) these real essences are unknowable. Even when considered more modestly, as collections of properties that co-exist in a common substrate, our complex ideas of substances are merely partial approximations, since it is clear that they include only those features we have most commonly observed; it always remains possible for us to be surprised by the discovery of another property that belongs just as surely in the same being.

[Essay II xxxi 6-11] As always, ideas derived from experience can be no more adequate than the experience itself, and with respect to natural things our experience is limited.

Although he maintained that truth and falsity are most properly regarded as characteristic of propositions, Locke granted that ideas are sometimes said to be true or false (better: right or wrong) by virtue of the role they play in the formation or assertion of such propositions. [Essay II xxxii 1-5]

It is the relation between ideas and the words used to signify them that matters for this representational criterion. Because of their familiarity in our experience and the frequency of our discourse about them, our ideas of natural substances and their qualities are often truly signified by the common terms we employ to designate them. [Essay II xxxii 6-10]

It is the ideas of mixed modes, manufactured independently in the minds of individual thinkers and lacking any external referent, that are most commonly false in this linguistic sense, because we do not agree on the signification of their names. [Essay II xxxii 11-13]

On the whole, then, Locke believed that ideas provide a vital but imperfect foundation for human discourse and knowledge. As we continue our study with an examination of his philosophy of language and of knowledge, we'll be reminded of the limitations imposed by the reliability of ideas of each type.

©1999-2002 Garth Kemerling.Last modified 27 October 2001.Questions, comments, and suggestions may be sent to: the Contact Page.

Words

Since the significatory function of words is especially vital for the achievement and expression of human knowledge, Locke devoted an entire Book of the Essay to his careful examination of "the Nature, Use, and Signification of Language." [Essay II xxxiii 19] On Locke's view, language is the instrument of all human social interaction, for the employment of which we are provided with three crucial requirements: First, we have appropriate physical organs with which to form a great variety of articulate sounds.

Second, we have the capacity for using these sounds as "Signs of internal Conceptions," with which we communicate our thoughts to each other. Third, in order to avoid the inconvenience of trying to have unique names for everything, we have the ability to employ words as general terms applied commonly to many particular things. [Essay III i 1-3]

Lesser creatures lack the third requisite and superior beings somehow communicate (in ways we cannot imagine) without the first, Locke supposed, but human beings rely upon spoken language as a primary vehicle for communication. Like thought itself, language is designed to serve the practical needs of human life.

Language

The question, then, is how we achieve our communicative goals, and Locke proposed a deceptively simple theory: words signify ideas. Since my own ideas are inaccessible to others, I employ the articulate sounds of human speech as extrinsic sensible objects by means of which to convey my thoughts to others. The absence of any universal human language, Locke argued, shows that the connection between each word and the idea it signifies is not natural but purely conventional, an association established by "voluntary Imposition." [Essay III ii 1-2]

Frequent repetition renders this association so intimate that some ideas may be induced more easily by words than by their referential objects, yet the freedom with which individuals form the requisite association often makes it difficult for a speaker to be sure that the appropriate idea has actually been induced in a hearer. [Essay III ii 6-8]

Both the equivocal use of terms and the invention of needless jargon by the learned, Locke supposed, amount to violations of the conventional agreements upon which language is properly founded. [Essay III x 5, 11]

There is a fundamental problem here: since ideas differ from person to person, and even in a single individual at different times, and since the association of word to idea is purely voluntary, even when secured by conventional agreement, it follows that the correct signification of a particular use of any word depends wholly upon the particular idea in the mind of its speaker, to which the hearer has no access except through the mediation of the word. [Essay III ii 2-4] On this view of language,

it is always possible that two people interact with each other verbally even though they do not achieve genuine communication because they do not associate similar ideas with the words they employ. In principle, I can never be sure that the sensory idea you experience in association with the word "red" is at all like the one I have when I use that word.

Locke officially granted only two kinds of exception to the general principle that every meaningful word signifies some idea. The first kind of exceptional case includes negative terms-"nothing" or "ignorant," for example. We don't need a distinct idea in mind for each of these words, Locke held, since we already have the positive idea whose absence each negative term signifies. [Essay III i 4] The other, more significant, exception comprises syncategorematic terms, what Locke called "particles"-such words as "is," "of," and "but."

Such words are not associated with particular ideas, Locke supposed, but "are all marks of some Action, or Intimation of the Mind." Thus, on theoretical grounds, these terms are techinically insignificant, but serve the important role of providing helpful guidance for interpreting the mental dispositions upon which human reasoning so often depends. [Essay III vii]

General Terms

The use of general terms is one of the most vital features of linguistic competence. Even though existing things-including words themselves- are invariably particular, Locke held that three considerations demand that some words be employed in a general signification: having a distinct word for each and every particular thing would exceed our linguistic and intellectual capacities;

unique names for particular ideas would make it impossible to communicate with others who do not share exactly the same ideas; and the most significant varieties of knowledge are precisely those that comprehend many particulars under some general rule. Thus, we have a natural prejudice in favor of general terms. Only under special circumstances will the practical needs of life override it in favor of having distinct names for particular things. [Essay III iii 1-5]

Since the signification of any word is an idea, Locke supposed that the signification of every general term must be an abstract idea, employed by the mind in reference to many particular things. General and Universal, belong not to the real existence of Things; but are the Inventions and Creatures of the Understanding; made by it for its own use, and concern only Signs, whether Words, or Ideas. Words are general, as has been said, when used,

for Signs of general Ideas; and so are applicable indifferently to many particular Things. [Essay III iii 11] Thus, on Locke's view, the classification of particular things into sorts or kinds, denominated by general terms, has no direct foundation in nature; it is, instead, the end result of our own complex process of abstraction. [Essay III iii 12-14]

Essences are nothing more than abstract ideas formed by the mind to provide significance for general terms, and their presumed immutability derives from our own power to retain the precise content of an abstract idea even in the absence of conforming instances. [Essay III iii 19-20] Formed by the mind, abstract ideas may differ from person to person, resulting in disputes over the applicability of the general terms that signify them. For "ordinary Conversation," however Locke held that minor variations of this kind may be tolerable, even for instances when one person's conception happens to be far more comprehensive and accurate than the other's. [Essay III vi 20, 31]

Even though our urge to classify things into sorts arises from the observation of genuine similarities among them, then, it is satisfied only by the provision for practical communication with general terms that designate abstract ideas. Every distinct abstract idea creates a distinct species of things by governing the applicability of a distinct general term. [Essay III vi 38]

As Locke pointed out, this makes it easier for us to classify artifacts than to discover the presumed genera of natural things. Having devised the artificial things themselves, we already have a conception of their structure and operations, and this provides a rich basis for the abstract ideas by means of which we sort them. [Essay III vi 40-43] It's easier to be clear about what "clocks" are than it is to decide whether or not "cardinals" belong to the "finch" family.

In general, Locke denied that human classificatory activity is ever governed by reference to natural kinds. The species of mixed modes by means of which we differentiate among human actions, for example, are devised entirely for our convenience in communication; the abstract ideas that represent such actions are held together precisely by their association with the general terms that signify them in ordinary speech. [Essay III v 9-11]

Even in the case of substances (to which we will return shortly) Locke argued that a mistaken belief that our classification must be drawn by reference to natural kinds or substantial forms amounts to an abuse of language, since it is founded upon a pair of false suppositions: that there are such natural kinds and that we have knowledge of them. [Essay III x 20-21] The false expectation that classification is natural can only lead to profound skepticism about the possiblity of general knowledge.

Real and Nominal Essence

Locke drew a careful distinction between two senses of the word "essence." Understood etymologically, as the very being of a thing, the real essence can only be that particular internal constitution from which all of the perceived qualities of a thing causally flow. Understood scholastically, as the ground for human classification of things into species and genera, on the other hand, the nominal essence is nothing more than the abstract idea, conformity with which justifies application of the associated general term. [Essay III iii 15]

For both simple ideas and modes, he supposed, these two "essences" invariably coincide, but for substances they are always different. Sortal terms for kinds of substances signify abstract ideas whose content rarely even appears to coincide with an internal stucture or compositions from which their features might be presumed to flow.

The nominal essence signified by the general term "human being," for example, would just be the idea by comparison with which we recognize individual instantiations of our own species, not the unknown (and perhaps unknowable) genetic structure that generates the development of a human life. [Essay III vi 1-3]

Locke held out for the possibility that there is some real essence (perhaps a set of primary qualities) that do in fact generate all of the observable features (many of them secondary qualities and powers) that make individual things what they are. But since our knowledge includes neither a direct awareness of that inner essence nor an understanding of the causal processes by which it produces ideas of its features in us,

it would be pointless and counter-productive to suppose that such knowledge is required for the practical task of classifying them. [Essay III x 17-18] When we try to use general terms to speak about the true nature of either material or thinking substances in themselves, then, we are pursuing a fool's errand and must of necessity fail to accomplish what we set out to do.

The practical use of general terms to sort out varieties of familiar substances is a different process altogether. Here, Locke supposed, a speaker observes the natural regularity with which certain features are observed to occur together, combines and abstracts the ideas of these features to form the abstract idea of a kind of substance, associates a general term with this abstract idea, and then applies the term to new instances of the same experience, without claiming thereby to fathom the true nature or real essence of such things. [Essay III vi 46-48]

In order to serve our practical communicative needs, Locke supposed, the process must employ nominal rather than real essences.

We find it convenient to associate a single general term to each abstract idea, rather than repeatedly generating a tedious list of specific features. But it follows that the distinction of species is entirely a product of the human understanding rather than a fixed aspect of nature itself. [Essay III vi 34-35]

On the one hand, this makes the (nominal) essence genuinely ingenerable and incorruptible: each general term designates an abstract idea whose pristine purity is unaffected by the existence or non-existence of any things that conform to it. [Essay III vi 19-20] On the other hand, it also makes the distinction of species perfectly arbitrary, framed for the convenience of human discourse rather than out of any respect for the real essences of natural things. [Essay III vi 38-41]

For each sort of substances, we choose a few "leading Qualities" as characteristic marks of such things, to which we commonly add a few other features-including especially the active and passive powers- that we have found often to coexist with these marks, forming the nominal essence by virtue of which we determine the applicability of a general term. [Essay III xi 19-21] When it comes to the classification of substances into sorts, it's all about us.

Simple Ideas and Modes

Although simple ideas carry with them a presupposition of real existence, Locke held, the names of simple ideas signify both the real and the nominal essences of the qualities they represent. [Essay III iv 2-3] Like the simple ideas themselves, which are involuntarily received in perception, the names of simple ideas have non-arbitrary content.

We find it difficult (and, usually, unnecessary) to classify them into sorts, and when we do so-as, for example, with colors or sounds-it is typically by reference to their perceptual origins rather than any supposed ideational similarity. [Essay III iv 16-17] Similarly, because each simple idea is a uniform perception, easily retained and intended to conform only to itself as an archetype, our names for simple ideas are rarely vulnerable to imperfection; the more simple the idea, the less likely we are to misuse the word that expresses it. [Essay III ix 18-19]

One consequence of all this is that the names of simple ideas are indefinable. At peril of an infinite regress, the provision of verbal definitions must ground out on some indefinable terms, and since simple ideas have no component parts that could be assembled under the direction of an appropriate definition, their names are perfectly suited to that role.

Scholastic efforts to offer definition of such simple ideas as motion or light, Locke argued, are ludicrous precisely because they so patently fail to produce any new idea in the minds of those who hear them. Imagine the comparable folly of trying to provide auditory definitions of visual ideas, or vice versa. [Essay III iv 4-11]

The names of mixed modes, on the other hand, are general terms that signify abstract ideas governing species of human actions. These names clearly are definable, since it is always possible in principle to offer a comprehensive list of those simple ideas which, assembled together by the mind, would constitute the appropriate complex idea.

That's why we don't need to witness an act of sacrilege or experience the resurrection of the dead in order to understand what kind of events those terms would signify. [Essay III v 1-5] Thus, Locke supposed that the initial formation of the abstract idea (and the stipulation of the name associated with this mixed mode) can be freely performed without any possibility of error.

It is only the subsequent use of the same word by other members of the same language-community that become vulnerable to mistake because they may fail to associate the word with the already-intended idea. [Essay III vi 43-45]

Here, even more obviously than in the case of substances, our acts of naming and classification are purely arbitrary, lacking any natural foundation. We do not discover the categories of human action (or their moral significance) as existing patterns of the natural world, but rather invent them in accordance with our own decisions about how to pursue practical life amongst one another. [Essay III v 6-9]

The vocabularies of morality, religion, and law are entirely of our own devising. This renders the use of such terms less problematic, Locke noted, and makes their misuse and confusion even less excusable.

©1999-2002 Garth Kemerling.Last modified 27 October 2001.Questions, comments, and suggestions may be sent to: the Contact Page.

Human Knowledge

Having explained the origin of our ideas and the use of words to signify them, Locke was prepared to consider the nature of human knowledge. He began with a simple definition: Knowledge then seems to me to be nothing but the perception of the connexion and agreement, or disagreement and repugnancy of any of our Ideas. In this alone it consists. [Essay IV i 2]

This definition gives rise to an obvious objection: if all human knowledge were wholly concerned with ideas, then it would lack an adequate foundation in reality and there would be no difference between the wise contemplation of philosophers and the fanciful but coherent imagination of the insane. Locke's response was two-fold: with respect to general knowledge, he boldly defended its detachment from anything other than our ideas, but with respect to knowledge of particulars he tried to show that there is a legitimate cognitive state that "goes a little farther than bare Imagination." [Essay IV iv 1-2]

Actual knowledge occurs only when we are actually perceiving the agreement in question, Locke supposed; our inclination to assent to what we've known in the past but are not presently attending to he called habitual knowledge. This capacity is clearly important for the development of learning generally; we can't focus on everything at once,

and it makes sense to rely upon our memories for general truths we have mastered on some occasion in the past. [Essay IV i 8-9] Thus, it makes sense to say that I know (habitually) the multiplication tables even at moments when I'm thinking about other things, provided that I can, upon challenge, call to mind the product of 8 and 7. The more crucial issue about human knowledge is to explain how it occurs in the first place.

No Knowledge is Innate

One account Locke unambiguously rejected from the outset is the supposition that human knowledge is innately inscribed. Noting the remarkably wide-spread agreement of individual human beings in their acceptance of both speculative and practical principles, the innatist argues that universal consent implies an innate origin.

Locke's response was two-fold: He denied the supposed fact of universal consent, supposing this to demonstrate the falsity of the innatist view. What is more, Locke argued that if there were any genuine instances of universal consent, they would more naturally be explained by universal possession of an intellectual faculty or by acquisition through some universal experience. [Essay I ii 1-2]

Granting that if general truths about logic were innately know by all human beings, then they must also be universally accepted, Locke emphatically denied the consequent. If the innatists were correct, then children (and mental defectives) would be the most pure and reliable guides to logical truth; but they are not. [Essay I ii 24-27] Of course the innatist reply to such counter-examples is to suppose that assent to innately inscribed principles is delayed until each individual is able to employ the faculty of reasoning.

But why should this be? Either reason is necessary for the discovery of such principles, in which case they are not innately known, Locke argued, or else reason and logic are merely coincidental features of human development, in which case both seem frivolous. [Essay I ii 6-13] Surely, in fact, the use of reason is properly concerned with our assent to general truths.

Locke agreed with the innatists that there is a significant distinction between truths to which we assent immediately upon first framing them on the one hand and, on the other hand, truths that require our careful consideration. But this distinction between self-evident and acquired knowledge, he supposed, doesn't correspond to the innatist identification of the most fundamental truths.

We assent to specific instances at an earlier stage of development than to speculative maxims themselves, and this is most easily explained by the fact that we acquire the particular ideas involved in the former long before we have manufactured the abstract ideas required for the latter. [Essay I ii 14-19] Careful attention to the development of knowledge in individual cases clearly shows it to involve the gradual acquisition of the requisite ideas, perception of whose agreement or disagreement constitutes knowing in each instance.

Achieving Certainty

Locke's definition of knowledge as perception of the agreement (or disagreement) of ideas clearly indicates two fundamental criteria for acquiring knowledge: first, we have to have the requisite ideas, then we also have to perceive the connection between them. Failure on either of these counts will leave us short of the certainty characteristic of genuine knowlege. [Essay IV iii 1-2]

The extended genetic account of our ideas in Book II of the Essay was designed to assist in satisfaction of the first criterion, by helping us to acquire a suitable stock of clear and distinct ideas about many things. But even where our ideas are amply clear, we may fail to achieve certain knowledge if we are unable to recognize the ways in which they are related to each other. [Essay IV ii 15]

Consider, for example, how the two criteria apply to specific areas of possible human awareness: Our passive reception of simple ideas from external objects provides only practical assurance of the existence of the objects themselves, so our knowledge of material qualities and substances is always limited in certainty.

But non-substantial complex ideas refer to nothing outside themselves, so any connections we perceive among them are "infallibly certain." For this reason, as we'll see later, Locke held that all mathematical and moral reasoning is characterized by perfect certainty. [Essay IV iv 4-8]

What Locke's definition clearly demands is that all knowledge is relational in structure, or propositional in form; it invariably involves "the joining or separating of Signs, as the Things signified by them, do agree or disagree with one another." [Essay IV v 2] But since both ideas and words are properly understood as signs, Locke believed it vital in principle, though often difficult in practice, to distinguish between truth in thought and truth in language.

Ultimately he distinguished between mental propositions in which ideas are perceived to agree and verbal propositions that affirm the agreement of words. In both cases, the criterion of truth is that the relation of the signs conforms to a more fundamental agreement that holds among the things they signify. [Essay IV v 3-5] Naturally the two kinds of proposition are connected with each other.

Certainty about the truth of a verbal proposition requires that it accurately express the agreement of the ideas signified by its terms; certainty about the knowledge itself further requires that we actually perceive that agreement among ideas. [Essay IV vi 3]