A lot of times we find ourselves in a path that we must take. This is the path of predestined things in our lives, such as our ethnicity, family, language and physical features like our height and weight. On the other hand, there are many times when we are able to choose from amongst the many paths that lie ahead of us. The first question that comes to mind is what should I do and what path should I choose? These questions that are comprised of words like why, which, what, etc., clearly illustrate our free will as human beings.
As far as whether this free will is limited or not, one must say that in reaching the final goal, we are not the ‘Illah Tāmmah (complete cause), but nor do we not have any effect at all. In other words, even though our free will plays the role of an ‘Illah Nāqisah (part of the cause), meaning that there are other conditions that must be met for us to reach the intended result, it is still instrumental in doing so.
Like everything else in this world, every act that we intent to do is a phenomenon and for it to actually take place, it is in need of a cause. Knowing that man is only one factor amongst many others, other factors can also affect his actions. For example, for one to eat a piece of bread, not only does he need to will such a thing and carry it out with his hands and mouth, but a piece of bread must also exist and be available at the intended time and place. Without these conditions being met, eating the bread would not take place. Also if all the conditions are met and the complete cause exists, then the result will necessarily take place. (The complete cause of something means the existence of all the necessary factors and causes of something taking place or coming into existence)
Allah Almighty has decreed that man’s will have effect in this world. If an incident has five conditions that need to be met to take place, one of those is man willing it to happen. For example, to turn on a light, all the required systems must be in place, including the switch, wires, lamp, the connection between the wires, the source of electricity and the electrical flow itself. If all the other conditions are met we can be effective in turning the light on by turning the switch. In this example, let us say that turning the switch represents our free will and God has willed that as long as one hasn’t turned the switch of something, for its light not to turn on (in voluntary actions). Also, just because the existence of something becomes necessary upon the existence of its complete cause, doesn’t mean that the relation between it and part of its complete cause isn’t contingency. It is true that in the previous example, if all the different factors existed, then the light would have to turn on, but is it necessary for the person to turn the switch on? Or is it simply possible? The answer is clear. It is simply possible for the person to turn the switch on and if all of the incomplete causes gather to form the complete cause, the light will necessarily turn on. This possibility between man’s will and turning the switch on does not contradict the necessity of the light turning on when the complete cause exists.
Our simple understanding of this issue also proves this opinion, because we see that even an uneducated person considers things like eating, drinking, coming and going different than feeling well or sick and being tall or short. The first group are considered actions that man’s will plays a role in and therefore, people praise or blame individuals for carrying them out, while the second group are considered inevitable matters that man has no responsibility in regard to them.
During the time of Imam Sadiq, two major opinions were presented by Sunni scholars in this regard. A group of scholars believed that man is forced in the actions he carries out and does not have free will. Another group believed that God has no control over man’s actions and that man has complete free will.
However, according to the teachings of the Ahlul-Bayt, which are in accord with the apparent meaning of Quranic verses, man has free will, but at the same time, he is not completely independent. This is because he was granted free will by God in the first place. In other words, God wants an action to take place by its complete cause, a part of which is man’s will and choice. As a result, the existence of an effect is necessary if its cause is complete, and is contingent (may or may not happen) compared to the partial and incomplete cause.
Useful books to refer to:
1- Ensan Shenasi, Mahmud Rajabi, chapters 5 and 6.
2- Amuzeshe Falsafe, Misbah Yazdi, vol. 2, lesson 69.
3- Divine Justice, Murteza Mutahhari
 Either a cause necessitates the result by itself and does not need anything else to do so, or its existence is necessary for the result, but is not enough and also requires other causes to necessitate the result. In the first case, the cause is called illah tammah (complete cause), while in the second, the cause is referred to as illah naqisah (incomplete cause).
 Tabatabai, Sayyid Muhammad Husayn, Shiah dar Eslam, p. 78.
 Ibid, p. 79.