According to epistemologists, the intellect is a faculty which cognizes general concepts and has two functions: intuition (cognition of self-evident propositions) and reasoning (discovery of theoretical knowledge). The intellect or reason is of two kinds: theoretical and practical. The theoretical reason cognizes the facts—what is there—and the practical reason has a prescriptive or imperative function—what ought or ought not to be done.
According to some hadiths, the intellect is particularly significant, counting as God's proofs for human beings along with the prophets (a). Also, along with the Qur'an, the tradition, and consensus, the intellect counts as one of the Four Sources for the deduction of jurisprudential rulings in the Shiite jurisprudence. Shiite scholars prove some principles and rules of jurisprudence and principles of jurisprudence on the basis of intellectual reasoning.
As a Source of Knowledge
Epistemologists consider the intellect as a source of knowledge, just like sensory perception. They maintain that human beings can cognize general concepts through the intellect, as they can perceive particular things through the sensory perception.
In epistemology, two functions are attributed to the intellect: an intuitive function of cognizing the facts, and a discursive or argumentative function of discovering new information on the basis of previous knowledge. The former leads to the cognition of self-evident propositions, and the latter leads to knowledge of theoretical, non-evident facts.
Theoretical and Practical
The intellect or reason is categorized into theoretical and practical.
The theoretical reason functions to cognize facts, and the practical reason functions to prescribe or specify what ought or ought not to be done. Some people believe that a human being does not have two separate intellects; rather they have a single faculty which has both functions. According to this view, the difference between theoretical and practical reason goes back to what is cognized, rather than the faculty itself.
Place for Imamiyya
According to Morteza Motahhari, the intellect is not as highlighted and emphasized in any religion as it is in Islam. According to a hadith from the Prophet Muhammad (s), all the good is cognized by the intellect, and a person who has no intellect (that is, who does not reason) has no religion either. According to a hadith from Imam al-Kazim (a), the intellect is considered as an internal proof (hujja) of God for people as prophets (a) and Imams (a) are external proofs of God for them.
According to the Shi'a, both the principles of the religious beliefs as well as some principles of jurisprudence, and even some jurisprudential rulings, are proved or discovered by the intellect.
Place in Jurisprudence
Along with the Qur'an, the tradition, and the consensus, the intellect counts as one of the Four Sources for the deduction of jurisprudential rulings. In the process of their ijtihad, Shiite jurists frequently draw on the intellect and reasoning. Some of its uses in jurisprudence are mentioned in principles of jurisprudence. Here are some of the functions of the intellect in the process of deducing jurisprudential rulings:
- Source of jurisprudential rulings along with the Qur'an and the tradition: the intellect or reasoning is sometimes an independent source for jurisprudential rulings, such as rulings discovered through rational goodness and badness (al-husn wa l-qubh al-'aqliyyayn), and is sometimes a supplementary reason along with another jurisprudential ruling, such as cases in which a new jurisprudential ruling is discovered through a relation of implication between a jurisprudential ruling and a rational principle.
- Proof for the reliability of religious texts: a condition for the reliability of, and the legitimacy of acting upon, hadiths is that they do not contradict an obvious rational or intellectual principle. For example, if there is an obvious rational reasoning for the infallibility of the Prophet (s), then any hadith negating the Prophet's (s) infallibility should be considered as unreliable.
- Indirect contribution to the deduction of jurisprudential rulings from the Qur'an and the tradition: some jurisprudential principles with which jurisprudential rulings are deduced from the Qur'an and the tradition are discovered by the intellect.
- Ḥusaynzāda, Mabānī-yi maʿrifat-i dīnī, p. 38.
- Malikīyān, Rāhī bi Rahāyī, p. 253.
- Ṣādiqī, ʿAqlānīyat-i īmān, p. 43.
- Ḥarrānī, Tuḥaf al-ʿuqūl, p. 54.
- Kulaynī, al-Kāfī, vol. 1, p. 16.
- Rabbānī Gulpāyigānī, Darāmadī bi Shīʿa shināsī, p. 139.
- Rabbānī Gulpāyigānī, Darāmadī bi Shīʿa shināsī, p. 144, 145.
- Muẓaffar, Uṣūl al-fiqh, vol. 1, p. 51.
- Ḍīyāʾīfar, "Jāyigāh-i ʿaql dar ijtihad", p. 230-234.
- Ḍīyāʾīfar, Saʿīd. 1382 Sh. "Jāyigāh-i ʿaql dar ijtihad." Naqd wa Naẓar 31, 32:427-442.
- Ḥarrānī, Ibn Shuʿba Ḥasan b. ʿAlī. Tuḥaf al-ʿuqūl. Edited by ʿAlī Akbar Ghaffārī. Second edition. Qom: Daftar-i Intishārāt-i Islāmī, 1404 AH.
- Kulaynī, Muḥammad b. Yaʿqūb al-. Al-Kāfī. Tehran: Dār al-Kutub al-Islāmīyya, 1407 AH.
- Malikīyān, Mūṣṭafā. Rāhī bi Rahāyī. Second edition. Tehran: Nigāh-i Muʿāṣir, 1381 Sh.
- Muẓaffar, Muḥammad Riḍā. Uṣūl al-fiqh. Qom: Daftar-i Intishārāt-i Islāmī, 1430 AH.
- Rabbānī Gulpāyigānī, ʿAlī. Darāmadī bi Shīʿa shināsī. Fourth edition. Qom: Nashr-i al-Muṣṭafā, 1392 Sh.
- Ṣādiqī, Hādī. ʿAqlānīyat-i īmān. Qom: Kitāb-i Ṭāhā, 1386 Sh.