Before answering this question it is necessary to mention that the subject matter i.e. "the relation between doubt and iman" is among the most controversial discussions in the field of religion studies in two branches of philosophy of religion and psychology of religion. This question presupposes that a constructive doubt may help shape the iman. This supposition itself is connected to four fundamental presuppositions:

First, there are two types of doubts: constructive and non-constructive.

Second, a constructive doubt can help shape the iman.

Third, a constructive doubt is not the complete cause of iman rather it is one of effective factors for iman to come to fruition.

Fourth, iman is not achieved overnight; it is achieved slowly and gradually. It is evident however that it can't be inferred from these four presuppositions that only a constructive doubt can help shape the iman; because first, having a path absolutely leading to a goal does not mean it is the exclusive path leading to the same goal. In other words, even if we are certain that a path will lead to a goal does it necessarily mean that the path is an exclusive path? Certainly not, second, we do not know what the questioner precisely meant by "a constructive doubt" versus "non-constructive doubt". However, if we consider the "constructive doubt" as a doubt that may help shape the iman and "non-constructive doubt" as an unfruitful one then it can be concluded that only "a constructive doubt" can help shape the iman.

Different viewpoints regarding these four presuppositions

The reason to mention these four presuppositions was to clarify the question, remove its superficial simplicity and point out other foundations and ideas on this issue irrespective of whether or not someone believes in it.

How a constructive doubt influences faith [iman]

Two major philosophical viewpoints in western philosophy have studied how iman is obtained by way of doubt. These two philosophical perspectives differ in what the standard for the value of iman is. The first viewpoint considers the value of iman in its rational certitude (external value) whereas the other viewpoint defines the value of iman as the doubter's paradoxical state (internal value):

1-Cartesian doubt or faith as intellectual and certain knowledge:

Rene Descartes (1596-1650), French mathematician and philosopher, sought to base Christian theology on a certain and scientific foundation as mathematics. To achieve this goal he established a new method in his "Meditations on First Philosophy" a method later known as Cartesian. The method Descartes thought of was to doubt everything. He wanted to have a fresh start in everything, therefore, he thought it was necessary to have second thought in all his information (including the sensible, rational concepts and auditory perceptions) then prove their truth by reasoning. Descartes' method was a reaction to extreme skepticism during renaissance dominating the European intellectual arenas. This method was also rooted in this attitude toward iman that iman is rational and demonstrative knowledge.

Therefore simply stated, Cartesian method means human should intentionally and methodically doubt the validity of all his beliefs and then try to rationally demonstrate all his beliefs based on this certain principle that "I cannot doubt that I doubt"

2-Kierkegaard's leap of faith or faith as a paradoxical state:

In his work "Fear and Trembling" Danish philosopher of religion, Soren Kierkegaard (1855-1813), who applied the term "existence" to his philosophy, has concentrated on God's command to Abraham to sacrifice his son, Isaac –Ismail in Islamic traditions - and contemplates on the concept of Abraham's iman. An act Abraham is obliged to perform following God's command violates his ethical beliefs –prohibition to slay his innocent child. Abraham should choose between following God's command and adhering to moral law. Here he makes his religious choice which means ‘suspending moral law’. This suspension as Kierkegaard states allows Abraham to achieve true fidelity and devotion to God. To avoid final hopelessness as a result of doubt, one should perform an act similar to a leap toward a religious life. To Kierkegaard, iman is to take risks. In contrast with Descartes' and Hegel's philosophy who believed they have reached a thoroughly intellectual understanding of human life and history, this Danish philosopher makes references to man’s vague and paradoxical state. To him, iman is not one hundred percent certitude and this kind of iman which is merely a result of intellectual contemplations is worthless, rather the true iman is in utter devotion to God's commands and endangering choice with no intellectual assurance even at the expense of suspending morality's ruling. Therefore in simpler terms, in this method the doubter ignoring the non-methodical and unwanted doubt that he is challenged with, he accepts God's command while he does not reject his intellectual doubt achieving iman this way. Kierkegaard writes: "To get free from temporal matters and obtaining eternal matters simply human courage is needed, however, I will certainly achieve it since after being in eternity I can't ignore it without facing the paradox. However to achieve all the temporal matters thanks to impossibility, a moderate and paradoxical courage is needed i.e. the courage of faith. Abraham did not leave Isaac by his faith rather he obtained him by faith."[1]

If looked at this issue from Muslim mystics' and philosophers' viewpoint, these philosophers' views are not the complete answer to this question as they suffer from setbacks and flaws. Basically the answer to this question has a different form. In his Mafatihul Gayb, Mulla Sadra writes:" Be aware that infidelity has various levels and each level of infidelity corresponds to a level of faith."[2] He enumerates four levels of infidelity as under:

1-Physical infidelity: one who rejects one of religion's essentials or one of shari'a's [religious laws] conspicuous rules.makeis ethic's ruilng. Here he cre he chooses his religious choiprinciple "

2-Infidelity of the soul: one's infidelity who still resides in material world  and has not yet journeyed to the divine realm.

2-Infidelity of the heart: a wayfarer (seeker) assumes that his entity is God's entity…this causes instability in iman while God's image has not been in the mirror of his entity rather it has reflected in it not has incarnated in it.

4-Infidelity of the spirit: It is a hidden shirk [polytheism] more concealed than any other type of dualisms and polytheisms and is the source of any shirk and infidelity and the root of any evil and harm.[3]

To explain this, Quran's viewpoint about the various stages of Islam, iman, certitude and levels of shirk should be mentioned. These vertical levels show that a true believer doubts as a mental obsession and a satanic and discouraging suggestion drives him away from himself, however he always seeks more supreme and intuitive knowledge. That is to say, when man is certain about the base of his belief of God he accuses himself of ignorance about the level of his knowledge in this field and questions all his knowledge by seeking a higher truth. This leads to his leap toward a more true and profound knowledge about his beliefs. This is not a doubt in God or beliefs rather it is a doubt about one's imperfection, deficiency and ignorance since one may consider himself as a religious person while he has indulges much of his ignorance in this regard. Therefore with a critic viewpoint about himself one should always try to discover the true religion. This viewpoint, even if called a doubt, is undoubtedly in contrast with iman rather it is a doubt in one's level of knowledge at the moment and seeking religion and a higher knowledge and certitude in future.

Now we look at this issue from another point of view. According to the Quran, the levels of the formation of Islam, iman and certitude is that merely accepting the concept of God without it entering one's heart and feeling is not iman rather this mental and verbal profession is just surrendering to a phenomenon called religion. Therefore iman is connected with the heart not mind.

Now we say that mind is intrinsically the center of doubt and suspicion and the heart is the source of certitude. Even in its most certain state about God, the mind can't grasp anything about God and has merely accepted the idea of God since God can't be known by mind. However, a sound and live heart shows humans the shortest path to know God. Consequently most of those who are proud of their subjective information have not progressed in the path of religion. On the contrary those who have faced the universe by their heart have simply discovered God.

Therefore when iman appears in one's heart he does not have the right to abandon this precious gem by a doubt suggested by mind. Many traditions which consider doubt as a negative phenomenon refers to this fact. Even more perfect humans do not violate their certitude by doubt. On the contrary, weak people are always trapped in doubt and confusion.

Therefore the mind which always has a doubtful and obsessive state is vulnerable to satanic suggestions and inculcations –as long as the person with this mind has not reached perfection. Thus after iman is formed in heart Cartesian and intentional inculcation of doubt emanating from mind does not have a constructive state.

Nevertheless we know that after the formation of iman, the heart always seeks certitude and observation of the truths. This desire does not finish unless the heart achieves what it seeks. In this regard, Quran has brought up levels called "knowledge of certitude" and "vision of certitude"[4] and a true believer can't be in a state without seeking certitude and a lower state of iman unless he has achieved the final level of his belief.

Great individuals have been in Islam's history who while believing in God, sought certitude by heart all their life and questioned many eclectic subjects that have become popular under the title of Islam to reach the true religion observing the truth after many years of endeavor and struggle.

This doubt is one of the most blessed doubts since it is a doubt about popular beliefs which are in fact against the religion and not a doubt in religious beliefs. Many mystics have had this type of doubt about the popular beliefs in their society. They may have been accused for this reason. However this is a doubt about wrong materials which are considered among the mashhoorat of the society [issues known to be part of Islam which may in fact not be part of it] while we know that doubting the wrong issues called the truth is a prelude to the discovery of the truth.

Relevant index:

Source of Cartesian doubt theory, 2427, (site: 2538)

Doubt and Hesitation in Beliefs, 20727 (site: 19932)