As for the saying of the one who said, "Where does it (the soul) reside in the body?" Then there is no specification of any particular part of body for the soul, rather it flows through the body (as a whole), just as life, which is a temporal attribute ('arad), flows through the entire body. For life is conditioned by the soul, if the soul is in the body, it will have life, and if the soul departs from it, then life departs from it. And as for his saying "Where does intellect, reason (aql) reside within it (the body)?" Then reason is established with the soul that displays reason (grasps, understands). And as for the body, then it is connected (متعلق) to his heart, just as Allaah, the Most High said, "Do they not traverse through the Earth wherewith they have hearts with which they understand" (22:46). And it was said to Ibn Abbaas, "How did you acquire knowledge?" He said, "With an inquisitive tongue and a understanding heart (قلب عقول)."Comment
However, the word "heart" (قلب) (can be used) to intend the pine-shaped organ which is in the right side of the body... or (قلب) (can be used) to intend the interior of a person absolutely, like the (whole) interior of a wheat grain, almond or walnut. When this is intended by (قلب) then reason (عقل) is connected with the brain as well, and for that reason it has been said, "The intellect (عقل) is in the brain" as is said by many of the physicians and it has been narrated from Imaam Ahmad, and it is said from a faction of his associates too, (that) the foundation of intellect is in the heart and when it completes it arises to the heart. However, that which is correct (in the matter) is that the spirit (روح) which is the soul (نفس), it has a connection to this (the heart) and to that (the brain), and that which it is described of intellect (عقل) is connected to both this and that. However, the starting point of thought (فكر) and observation (نظر) is in the brain. And the starting point of desire (إرادة) is in the heart. And both knowledge and action can be intended by (the word) reason (عقل). For the foundation of knowledge and chosen action is desire (إرادة) and the foundation of desire is in the heart. And the one who desires cannot be desirous except after imagining (تصور) that which is desired. Hence, it is necessary that the heart imagines, and hence it will have this (imagination) and this (desire). And that (imagination) commences in the brain and its effects (after going to the heart) rise back to the brain. Hence, from (the brain) is the commencement and to it is the final completion. And both sayings (regarding the intellect) have a correct angle. (Risaalah Fil-Ruh wal-Aql pp. 53-55)
In light of these words we can say the following: The faculty of reason, intellect (عقل) is not isolated and specificied to just one organ in the body exclusively, rather it is ascribed to the soul and body combined and then in turn, as it relates to the body, it is "connected" (متعلق) to the heart and brain. Note also that (عقل) is not an independent entity but an attribute that can be absent or present and can have strength and weakness, abundance and scarcity in a person. Further, we should also bear in mind the definition of reason (عقل), which Ibn Taymiyyah explains on numerous occasions and the essence of that can be explained by the following summarization, "Reason is collectively: knowledge by which what is beneficial is distinguished from what is harmful and then acting upon the dictates of that knowledge, as in, what this knowledge necessitates of action, hence a person traverses the ways to attain what is beneficial and traverse the ways by which harm is avoided." Thus reason incorporates both knowledge (ilm) and action (amal), and underlying action is desire (iraadah). And because imagination and conception is required by the heart (for it to desire what it desires), then the brain plays that role since reflection, thought (fikr) and observation (thought) is processed through the brain, so that begins with the brain (from sensory input) and then that goes to the heart which then "desires" on account of what is brought to it and when that is completed in the heart it raises back to the brain again. The brain then implements what the heart desires since the brain is a delegated control system for the activities of the limbs and organs (hands, feet, vision, speech, thought). However, the seat of all of that is the heart, since it is the heart that is ultimately desiring and the brain is delegated to the implementation. The heart drives and the body follows. And in this processs, the brain contributes to the element of thought and imagination that is then input to the heart and when processed by the heart for the formulation of the desire (iraadah) the matter is sent back to the brain and the brain is the delegated control mechanism for verbal speech and physical action. With this, any confusion or doubts should be settled inshaa'Allaah, and it is clear that reason (عقل) is an attribute of the body as a whole inclusive of the soul, the heart and the body. However since the heart desires (iraadah) as a result of which chosen action arises, it is the seat and the driver. Because reason is defined as acting upon what one knows to benefit and refraining from what one knows to harm, then the heart, from this perspective, is clearly the seat of reason. Ibn Taymiyyah says in al-Majmoo' (16/36): "However, that which is praised is the beneficial knowledge whose possessor acts upon, for if the one possessing it does not act upon it, then he does not have aql (reason, intellect)." And Sufyan bin Uyainah (d. 198H) said (as relayed by Ibn Abi al-Dunya): "The one who knows good from evil is (not the one who is intelligent) but the intelligent is the one who knows good and follows it and knows evil and avoids it." In these quotes we understand that it is chosen action that defines true reason, and the foundation of that is the iraadah (desire) of the heart. In summary, (عقل) is an attribute that is said of the soul and body combined and as it relates to the body, it is produced through a combination of the heart and brain. Hence, it is not exclusive to any organ but is connected to the soul, heart and brain that collectively play a role in producing the attribute of intellect (aql) in a person, and within those roles, the heart is in the driver's seat and the brain is an accomplice and without the soul there is no life (hayaat), hence reason (aql) is said of all three. Note also, as already stated, aql (intellect) is an attribute and not a thing in and of itself that can be said to be "here" or "there". The attribute of aql arises when the soul, heart and brain function to provide thought, imagination, desire, choice, speech and action and if the result (verbal speech and physical action) is in accord with what benefits (and not what harms) then the attribute of aql is present, and this attribute can be present, absent, strong, weak, abundant or scarce in a person.
Written by Abu Iyaad 17th Dhul-Hijjah 1434H (22/10/2013CE)