Mirza Na’ini, one of the founders of modern principles of jurisprudence, was the first one to develop and defend this theory. According to an exposition of the lectures of Na’ini (Ajwad al-Taqrirat), this theory can be traced back to Mirza Muhammad Taqi Isfahani, the author of Hidayat al-Mustarshidin (a commentary work on Ma‘alim Al-Usul).
After Na’ini, our great master, the martyr Sadr, reconstructed this theory to meet the problems raised against the theory and, in an innovative way, developed it and called it "The Theory of Sovereignty". In what follows, we will briefly present the ideas of Na’ini and then will focus on the theory of sovereignty.
Na’ini starts his argument with two common sense laws that both can be affirmed after a short reflection: First Law: Will (iradah) of the free agent itself is not voluntary. Reflecting on the process of decision-making inside ourselves, we realize that after conceiving the act and affirming its benefit our will automatically comes into existence. Will is an inevitable outcome of conceiving the act and affirming its benefit. Na’ini says: "Surely, all those qualities that belong to the soul such as will, conception and affirmation are not voluntary ."[1]
In respect to God, it can be demonstrated that His will is not voluntary, because his essence is simple and free from any attributes accidental and additional to it. Therefore, will cannot be accidental to His essence, since it is in conflict with the simplicity of the essence. Will of God is identical with His essence and this implies that the Divine will is essential and it is self-evident that essential attributes are not voluntary. We find in an exposition of Na’ini’s lectures that: "Surely the will that is the complete cause of the existence of the effects is the same as His essence, and self-evidently His essence, the Exalted and the Glorified, is not voluntary for Him."[2]
Second Law: Human soul has complete sovereignty and authority upon its voluntary acts. In other words, man always feels very clearly that has complete power to make his decisions regarding his voluntary acts. Na’ini writes: "Surely, the soul has complete effect and authority on muscles without facing any obstacle in exercising its sovereignty."[3]
Na’ini concludes that there must be something between the will (iradah) and act. He calls this element "ikhtiyar". Ikhtiyar is an act of soul that takes place after the formation of iradah and its prerequisites. In this way, Na’ini argues for his position and adds that it is the only solution for the well-known objection of Fakhr al-Razi, who asserted that voluntariness of an act implies its involuntariness, since voluntariness of an act means to be caused by the will, but the will itself is determined by causes that produce it necessarily.
Na’ini responds to this objection by saying that the voluntary act is not caused by the will; rather it is caused by something, which occurs between the will and act, i.e. ikhtiyar (or talab). Ikhtiyar is not caused by the will; it is originated from the essence of the soul.
Na’ini believes that there is no necessary relation between ikhtiyar and the soul. Human soul in making ikhtiyar just needs some preponderating factor. For this it would suffice that the agent purses an end or goal in the act.
There are many objections to Na’ini’s theory. First, the difference between iradah and ikhtiyar is not known. If the ikhtiyar can escape cause-effect necessity why cannot iradah do this?
Second, Na’ini has not solved the problem in relation to the Divine acts, because ikhtiyar also cannot be additional to His essence and according to Na’ini himself the Divine essence is not voluntary for God. Now the question is: Does Na’ini believe that Divine acts are voluntary?! How does he treat the decisive and certain belief in His power and His willingness?
Third, is ikhtiyar or talab, which is the basis of Na’ini’s theory on voluntariness of acts contingent or necessary? Na’ini does not accept its necessity and takes it to be contingent. Therefore, it must have equal relations to both existence and non-existence and according to the law of impossibility of preference without a preponderant; it would be impossible for ikhtiyar to exist. There is no solution for this problem in Na’ini’s account.

Sadr and the Theory of Sovereignty
The difficulties in Na’ini’s theory led the great Ayatullah Sadr to reconstruct the theory and revive Na’ini’s claim with a new argument. To develop his theory of sovereignty Sadr first mentions some premises: First premise- Equal relation of act to existence and non-existence is a clear fact that no intuition or argument can disprove it. Every one of us clearly feels that after the completion of all prerequisites he still may or may not act. This is something that we understand clearly by our conscience and no argument can bring it into question.
Second premise- Necessity of prerequisites of an act leads to denial of free will and philosophers’ answers are not able to solve the problem. Their answers are just some linguistic rationalizations (such as saying that ikhtiyar means the agent’s consent or that the voluntary agent is the one that acts whenever he is willing and does not act whenever he is willing to do so) that cannot solve the conflict between reality of necessity and reality of ikhtiyar.
Third premise - The principle of causality is not demonstrated. So it cannot be said that it cannot have any exception, because it is rationally proved. This principle is indeed an intuitive and evident principle. To find the scope and extent of it we have to investigate its origins in our conscience.[4]
Based on the above premises, he argues that rationally any contingent being to come into existence needs an external factor. This factor can be either a cause that necessitate its existence or a voluntary agent that makes the act by his sovereignty. Having such an agent besides the act does rationally justify its existence. It is certain that the essential contingency does not suffice the existence of something. However, there might be something other than necessity that can preponderate the existence of a contingent being such as sovereignty.

The Definition of Sovereignty
Sovereignty or salatanah is an internal quality that we all understand. It is what we know by presence (‘ilm huduri). To conceptualize it we can use the expression: "The agent may or may not act". There is no necessity to act or not to act.
Sovereignty is similar to any of necessity and contingency from one aspect and different from each from the other. Sovereignty similar to necessity in being is rationally enough to justify the existence of a contingent being and leaving no need to look for something else. The difference between sovereignty and necessity is that with necessity an act loses its equal relations to existence and non-existence and necessity of existence takes its place, while with sovereignty the contingency remains the same. Necessity consists in the fact that the agent has to act or not to act, but sovereignty means that the agent may or may not act.
Sovereignty is similar to contingency in preserving the equal relations of the contingent to both existence and non-existence, but sovereignty is different from contingency in being rationally enough to justify the existence of a contingent being while with contingency the question remains why it must come into existence.
Having known that the sovereignty of the agent may substitute necessity and suffice the existence of a voluntary act which is the question at issue, reflection on our conscience and the way voluntary acts are issued from us shows clearly that the relation between us and our voluntary acts is one of sovereignty and not necessity. We as voluntary agents find that we have sovereignty upon our acts. We clearly understand the fact that even in circumstances in which all prerequisites and conditions of a voluntary act exist, it is not necessary to act. What we find deep in ourselves is this sovereignty upon our acts. It is up to us to act or not act and we are not compelled to do so.[5]

Evaluation
The theory of Na’ini as explained above seems to suffer fatal problems. It seems also that the martyr Sadr’s theory of sovereignty despite its beauties and firmness still has very important problems. Of course, this does not mean that Sadra’s theory of necessity is free from fundamental problems. In what follows, I will explain problems of both theories of Sadr and Sadra and then there will be a conclusion.

Objections on the Theory of Sovereignty
Granted that sovereignty suffices the existence of the act, would that also suffice its non-existence as well? If so, the problem would be that it leads to having both the existence and non-existence of the act at the same time. And if not, it would mean that the non-existence of the act must be impossible and its existence must be necessary, because non-sufficiency of sovereignty for non-existence and its sufficiency for existence damage the state of equality of existence and non-existence in the essence of the contingent and change contingency into the necessity of existence.
To interpret sovereignty as "may or may not act" is just a linguistic account that does not solve the real problem. In any case, with sovereignty the existence of the act as a contingent effect either remains possible or becomes necessary. If it remains possible, the question still remains why will it exist? Why did not contingency suffice the existence of the act in the first place? If it becomes necessary the problem with the theory of necessity would repeat.
Although the principle of impossibility of preponderance without a preponderating factor is not demonstrated and it is just self-evident, there must be a reason why something becomes self-evident. The reason here is the essential need of the contingent for a cause, that is the contingent as such is rationally impossible to exist or not to exist. The impossibility of existence and non-existence for the contingent as such is an essential judgment of our reason whose subject matter is non-necessity of existence and non-existence. This is a universal and essential judgment of the reason that has no exception like any other proved universal and absolute judgments.
What is the meaning of sufficiency in saying that the sovereignty is sufficient for the existence of a voluntary act? Our master, Sadr, uses the expression "may or may not act". If it means possibility of existence the problem is that this is something, which has been already there, and if it means necessity the problem is that this is the same idea involved in the theory of necessity.

Objections on the Theory of Necessity
This theory is against our intuitive feeling that both sides of the act even after the completion of all prerequisites are still equal to us as voluntary agents. We feel no necessity. This can be replied by saying that it is indeed an essential feature of ikhtiyar that at no stage the agent feels compelled or forced from outside, but this does not mean that his decisions are made arbitrarily and are not subject to any rational rules.
If our will and decision and all prerequisites are subject to the principle of cause-effect necessity how can we justify Divine reward and punishment. The answer to this is that in any case our acts are voluntary and this is rationally enough to make Divine reward and punishment just.
There is no evidence for our reason or conscience that demands ikhtiyar it self must be voluntary. The other way to answer is to say that volunatriness of acts depend on their emergence from a voluntary agent (an agent that has ikhtiyar), but the voluntariness of ikhtiyar is essential and cannot be removed. Even if a superior cause originates ikhtiyar cannot remove its voluntariness. Thus, ikhtiyar is ikhtiyar, even if it is necessarily brought into existence by its cause. The essence of ikhtiyar (like any other thing) neither can be given to it nor can be negated.
Therefore, a voluntary act is voluntary, though all its prerequisites are governed by the principle of causal necessity, and has all the characteristics of voluntary acts, such as appropriateness of reckoning and punishment.
There is no way to deny the universality of the principle of causality and cause-effect necessity just as voluntarinees of our acts cannot be denied. What Muslim philosophers, especially Mulla Sadra, have argued for the universality of the principle of causality and its necessity and their responses to the objections are sound, but further points have to be made.
1. The relation of the essence of cause to its effect is a comparative contingency, imkan-e bil-qiyas. Cause cannot be made necessary by its effect. As explained before, the effect is nothing other than belonging to and dependence on its cause. The effect receives necessity of existence from its cause and, therefore, the relation of the essence of effect to its cause is necessity caused by the other, darurate bil-ghayr.
2. In the material world there is no real originating cause (al-‘illah al-fa‘iliyyah) that grants existence. All material causes are preparatory causes (‘illat- i‘dadi) or material causes (i.e. potentiality for existence or recipients of existence). In immaterial world all originating causes are voluntary.
3. In the immaterial world where the voluntary originating causality exists the relation of the essence of cause to the effect is that of a comparative contingency, while the relation of the effect to its originating cause is that of necessity, since the effect is nothing other than belonging to and dependence on its cause.
4. Our mind abstracts the notion of sovereignty from the mutual relation of cause and effect, which is from one side imkane bil-qiyas and from the other side darurate bil-ghayr.
Therefore, the theory of sovereignty can be somehow reduced to the above-mentioned mutual relation. According to this account,there is a special relation between a voluntary agent and its effect that is a combination of comparative contingency of the cause and necessity (caused) by the other of the effect. This very relation is the one from which notions of sovereignty and ikhtiyar are abstracted. It is also the same relation that accounts for the appropriateness of reckoning, punishment and reward.
In this way the problems raised against the theory of necessity or the theory of sovereignty as discussed above or more generally against the relation of cause and freedom can be solved. Further explanation of this point needs a separate discussion.

Notes:
[1]Mirza Na‘ini, Ajwad al-Taqrirat, vol. 1, p. 91.
[2]Mirza Na‘ini, Ajwad al-Taqrirat, vol. 1, p. 91.
[3]Mirza Na‘ini, Ajwad al-Taqrirat, vol. 1, p. 91.
[4]Sadr, Mabahith al-dalil al-Lafzi , Vol. 2, p. 36 and handwritings of his lectures by Ayatullah Sayyid Kazim Ha’iri, P. 418.
[5]Sadr, Mabahith al-dalil al-Lafzi, Vol. 2, p. 37 and handwritings of his lectures by Ayatullah Sayyid Kazim Ha’iri, pp. 419 & 420.