The mind is the most valuable faculty that Allah (swt) has endowed man with and it bears different degrees and classifications.
1- Theoretical intellect: Whose job is to know about realities and judge about them.
2- Practical intellect: Controlling man’s actions is the responsibility of this subdivision of the mind; it distinguishes between the do’s and don’ts and in reality, is the basis of all sciences related to life and living. In other words, the question it is always answering is whether something should be done or not.
Since the mind is a phenomenon, as is with all other phenomena, it is limited, therefore its scope is also limited and one can't expect the unlimited from it. Therefore, the most it is capable of is learning of creation and knowing God limitedly, without being able to completely know God, who is unlimited.
The mind can have endeavors both in tashri’i and takwini fields and learn more of them, nevertheless, it isn't totally needless of revelation in either one. For instance, when it comes to the details of resurrection (which has to do with takwin), or the reasons behind Islamic rulings (an example for tashri), the mind comes short and is in need of revelation.
The term ‘aql’ in Arabic and its derivatives refer to understanding, receiving, and tying a rope to the foot.
In the Quran, it has been used for “understanding” and “comprehension”. In our hadiths, it usually refers to the faculty responsible for distinguishing, comprehending and pushing us to do good and preventing us from evil.
In normal usage, this term refers to a noncompound (basit) substance (jawhar) that people use to know and understand realities. Therefore, the ‘aql’ is the receiving and understanding of realities. In addition, it is also the guardian of the intellective soul (nafs natiqah) and where it (the intellective soul) gets its superiority and dignity from.
The aql has different levels and degrees:
1- The theoretical intellect (aql nadhari): We use this dimension of our mind to understand what is and what isn't regarding science, mathematics, logic and metaphysics (and to sum all of them up, speculative philosophy/theoretical knowledge).
2- The practical intellect (aql amali): This is where faith, decision, resolution and willpower are taken care of, and in other words, where practice and action begin.
3- The common aql (aql muta’araf): The part of the mind in which is responsible for everyday affairs and tries to maintain normal life. Most people use the term ‘aql’ only for this active and comprehending dimension of the mind.
In other words, the theoretical intellect’s job is to understand realities and make judgments on them.
The practical intellect’s job is to control and manage one’s actions, or to comprehend the do’s and don’ts; in reality, this intellect is the basis of all life-related sciences. The question it is always dealing with is “Should I do this or not?”
In Imam Sadiq’s (as) words, the practical intellect is pivotal in the servitude of Allah (swt) and is the means of earning paradise: “العقل ما عبد به الرحمن و اکتسب به الجنان”.
In the enlightening school of Islam, the mind has been given a very high status. In the tafsir of Al-Mizan, Allamah Tabatabai says: “The mind is the most noble faculty man bears.” Allah (swt) has invited us to make use of this gift over three hundred times in the Quran. From Allamah Tabatabai’s point of view, thinking and using the mind has a very high status, to the extent that in the Quran, Allah (swt) not even once has ordered his servants to do something blindly without contemplating first.
The scope of the mind
According both to Islamic and rational reasoning, the scope of the mind and intellect pertains to creation/creatures, phenomena that take place in nature, Islamic rulings and the limited knowing of God, meaning that man isn't capable of totally understanding God; the reason being that anything of temporal origin (حادث) cannot be unlimited, and since the mind is such, it is limited, thus not bearing the capacity to be able to completely understand and know God.
Nevertheless, it can understand the world and its phenomena and their underlying laws and make judgments about them.
Also, the mind is employed in deriving Islamic rulings; in fiqh (jurisprudence), the mind is considered one of the four sources for such, next to the Quran and Islamic tradition. In usul also (which are the principles and methods used for deriving Islamic rulings from the sources), the mind plays the role of understanding that the commands and prohibitions of God must be adhered to under the discussion of “intellectual goodness and badness”.
Of course, what must be kept in mind is that in Islam, in both the fundamentals and branches, there are matters that are beyond the mind that although the mind doesn’t reject, but at the same time can't comprehensively and completely understand, such as the main reasons for Islamic rulings (although the mind can do some theorizing about some of them) which have to do with the branches of Islam, or the details of resurrection, which is something related to the fundamentals of Islam. Thoroughly explaining this matter is something beyond the scope of this article.
In response to an inquiry by the French Henry Corbin regarding what happens when there is a contradiction between the mind and religion and tradition, Allamah Tabatabai states: “If the Quran has directly granted authority to the mind and confirmed it, there will never be any contradiction between the two.”
It can be concluded from one of Imam Ali's (as) sayings about the sending of messengers that not only aren't the mind and religion in conflict, but are in total harmony: “...و یثیروا لهم دفائن العقول...” ([Allah (swt) sent the messengers] in order for them to revive the buried of the minds [of the people]…).
In this valuable saying, Imam Ali (as) provides us with the core of the sending of messengers, which is to awaken the dead minds of the people.
The mind and fitrah of man is like a safe in which all realities and truths are contained in, that is why whatever the prophets say reads with the mind and logic. There is a principle in the science of usulul-fiqh (principles of jurisprudence), by the name of ‘the principle of necessitation in which says: “کل ما حکم به العقل، حکم به الشرع” (Whatever the mind rules, religion also rules). The opposite of this principle also applies, meaning that whatever religion rules, the mind also rules. This is why one of the four sources of Islam is the mind (of course it must be noted that there are some boundaries and observations regarding this source that must taken into consideration).
Therefore, the laws that the prophets and religion hand down to us are in no way in contradiction with the mind, what they tell us actually can be found deep down in our minds as well, the only problem is that sometimes these truths are covered and concealed as a result of Shaytan’s endeavors, making us unaware of them, and that is why the prophets came; to remind the people of what they already possess.
Conclusion: Religion and the mind are in harmony and intertwined, and there is no law in religion that contradicts the mind and fitrah. This is why man always seeks reasoning for whatever he wants to accept; reasoning that convinces him, and when that happens, he accepts. Till now, we learned that it is in the scope of the mind to comprehend and even make judgments about religious rulings this world and its various phenomena and its underlying laws. As for understanding who god exactly is in essence, the mind’s scope is limited and there is no way that it can totally comprehend what and how god truly is.
In this regards Imam Ali (as) says: “...لم یطلع العقول علی تحدید صفته...” (He didn’t make the minds of the people totally aware of His essence).
Since Allah's (swt) qualities are one with His existence, and his existence is never-ending and unlimited, His qualities of perfection such as knowledge, power, life, will, etc., are also all unlimited and never-ending. Thus, man can never totally understand each and every one of these qualities. In other words, since man is a limited creature, he can never learn of and totally understand the unlimited, and this is what Imam Ali (as) means when he says: “He hasn’t made the minds of the people totally aware of His essence”. Of course, this doesn’t mean that Allah (swt) has prevented us from knowing Him, because the imam (as) goes on to say in the same sermon: “و لم یحجبها عن واجب معرفته” (and He didn’t prevent them from the necessary amount they need to know of Him).
Imam Sadiq (as) says: “...فبالعقل عرف العباد خالقهم و انهم مخلوقون و انه المدبر و انهم المدبرون و انه الباقی وهم الفانون...” (…It is through the mind that the people know their creator and that they are His creation and that He is the one who manages their affairs and that they are the ones whose affairs are being managed and that He is the All-Living and that they are to perish…).
The mind understands that this universe has a lord and that He bears qualities of perfection (kamal) and glory (jalal). Understanding this much is the responsibility of the mind and it bears the capability for such and god hasn’t prevented it either, but understanding who Allah (swt) exactly is and the depth of His essence is something the mind is in no way capable of accomplishing.
 Mohammad Mo’in, Farhange Mo’in, the term عقل.
 Seyyid Jafar Sajjadi, Farhange Ulume Falsafi va Kalami, عقل.
 Kuleini, Usul Kafi, vol. 1, pg. 11.
 Ali Karaji, Estelahate Falsafi va Tafavute Anha ba Yekdigar, pp. 171-172.
 Abdullah Javadi Amoli, Fetrat dar Quran, vol. 12, pp. 29-30 and 397.
 Shahid Mutahhari, Dah Goftar, pp. 30-31.
 Abdullah Javadi Amoli, Rahiqe Makhtum, vol. 1, first section, pg. 153.
 Shahid Mutahhari, Dah Goftar, pp. 30-31.
 Kuleini, Usul Kafi, vol. 1, pg. 11, hadith 3.
 Muhammad Husein Tabatabai, Al-Mizan, vol. 3, pg. 57.
 Ibid, vol. 5, pg. 255.
 Shadi Nafisi, Aql Garayi dar Tafasire Qarne Chardahom, pp. 194-195.
 Mujtaba Maleki Esfehani, Farhange Estelahate Usul, vol. 2, pg. 279.
 Mohsen Kadivar, Daftare Aql, pg. 115.
 Nahjul-Balaghah, sermon 1.
 Seyyid Abdul-A’la Sabzavari, Tahdhibul-Usul, vol. 1, pg. 145; Muhammad Ridha Mudhaffar, Usulul-Fiqh, vol. 1, pg. 217.
 Nahjul-Balaghah, sermon 49.
 Kuleini, Usul Kafi, vol. 1, pg. 33-34.