The Shi‘a believe that reason is a reliable source of knowledge and in complete harmony with revelation. According to some hadiths, God has two proofs (hujjah), through which humans can understand His Will: the internal one which is reason (al-‘aql) and the external, which are the prophets. Sometimes reason is called, “the internal prophet” and the prophets are called “the external reason”. There is an established rule among Shi‘a jurists that whatever judgement is made by reason is the same as that made by the religion (shar‘) and vice versa. It is also unanimously accepted that one of the conditions of moral or legal responsibility is to have sound reason. If someone is insane, he is not considered as responsible for his actions. What is expected of the people in religion also varies according to their mental and rational capacity. Those who are very clever and intelligent are expected to be more prepared, pious, and obedient than those who are lay or ignorant.

According to the Qur’an, God requires all human beings to exercise their rational faculty and to ponder on His signs and communications in the universe. On many occasions disbelievers are condemned because of their failure to think or to act according to rational requirements. For example, they are condemned because of their blind imitation of their ancestors, and there are many verses with rhetorical questions, such as: “Do not they think?!” (36:68), “Do not they ponder on the Qur’an?!” (4:82; 47:24) and “In these, there are signs for those who are thoughtful” (13:4; 16:67; 30:28).

In general, reason contributes to religious studies in three major areas: The first is in understanding the realities of the world, such as the existence of God, the truth of religion and scientific facts. The second is in introducing principles of moral values and legal norms, such as the evil of oppression and the good of justice. The third is in setting up standards and logical processes of reasoning and inference. All these three roles of reason are recognised and, indeed, recommended by Islam.

In contrast, the role of revelation or the Scriptures in religious studies can be summed up as follows:

  • confirmation of the facts that are already known by reason;
  • introducing new subjects that are not known by reason, such as details of resurrection and detailed accounts of moral and legal systems;
  • providing sanctions through the religious system of reward and punishment.

To conclude I should mention that there is nothing irrational in Islam. Of course, one has to distinguish between certain and decisive rational judgements, and one’s guessing or personal opinions. If there is a case in which it seems that rational judgement is in conflict with certain religious positions, one has to accept that there must be a mistake in at least one side: either it was not a real judgement of reason or it was not a religious law. God never misleads people by telling them to do something through the prophets, and the opposite thing through our God-given reason. There have always been some judgements attributed to reason and taken as contradicting religious positions that after close consideration have proven to be contrary to decisive rational premises.

Discovering Shi’i Islam Mohammad Ali Shomali 9th Edition