Intellect as Immaterial

For Aristotle, living things are understood as composites of body and soul. Body, which is matter, is informed by soul, which is form. Matter is also potency, or that out of which something is made, and form is act, or that which makes the matter an actual substance. Following this conceptual correspondence we can say that body, as matter, is potency, and soul, as form, is act. The body and soul composite is merely a specific kind of potency and act composite, namely, the kind proper to living things. Aristotle discusses the different powers of soul and then distinguishes living things according to the powers of soul most proper to them. Plants, for instance, have a nutritive or generative soul, while animals have a sensitive or perceptive soul. Human beings, however, have both the nutritive and sensitive powers, but neither of these are most proper to human beings as such. For humans, the power to understand, commonly referred to as the intellect, is what characterizes soul. There is a difference, though, that divides the human soul from the souls of animals and plants and it is found within Aristotle’s descriptions of each. Whereas the nutritive and sensitive powers require bodily organs in order to be actualized, the human soul cannot have any such organ.
    When Aristotle is discussing understanding he compares it to perceiving, both of which somehow consist in the reception of some object. This power of understanding, intellect, is characterized primarily by its ability to receive form. As something receptive, intellect is in potency with respect to all of the things which it is able to understand. While it is understanding something, or after having understood something, the intellect is, in a sense, actually what it understands, it contains within itself the form of the object of its understanding. This presents us with a problem.
    Remember that the body and soul division is a specific kind of matter and form division, the latter being found within all material reality and not just in living or organic things. All material substances are, by nature, composites of matter and form. But if the intellect, like matter, is able to receive form, then the intellect, like matter, would actually become the substance in question. For some matter to be in the possession of a certain form, a cat, for instance, is nothing more than actually being this same composite substance. For some matter to be informed by the soul of a cat is just what it is to be a cat. This distinction is at the heart of Aristotle’s ontology, but when applied to the intellect it seems incoherent. If understanding what it is to be a cat is identical with saying that my intellect is in the possession of the form of a cat, then the intellect, if it requires a bodily organ, upon understanding what a cat is, would quite literally become a cat. This is obviously not the case, though. The intellect is able to understand all types of forms and yet is never actually a material substance informed by the understood form in question. The implication, then, is that the intellectual power of the human soul cannot possibly require a bodily organ in order to actualize itself. Hence the intellect must be immaterial.


  1. The implication, then, is that the intellectual power of the human soul cannot possibly require a bodily organ in order to actualize itself. Hence the intellect must be immaterial.

    Okay, after understanding the form of a cat, my intellect does not become a cat. But where does the human brain fit in to this idea of not requiring "a bodily organ in order to actualize itself"? Is the fact that the human intellect is aware of its dependence on the brain further evidence of your assertion?

  2. Bodily organs are required for human understanding because all human knowledge begins with sensation. So to interpret "not requiring a bodily organ" to mean that human understanding does not involve any material operations is false. In fact, Aquinas says that, in our current life, the intellect will always need recourse to imagination, a material operation, in order to understand things.
    See Article 7 here:


    Human knowing, though, is a process, and so although it may begin with sensation, which would ultimately include brain activity, it does not end there. The intelligible species is abstracted from the sensible image, and this intelligible being is utterly formal. The active intellect must make that which is potentially intelligible actually intelligible, and once it is possessed by the intellect it exists in an immaterial, universal, and necessary way.

    So the human intellect is immaterial because its per se operation cannot be the act of a bodily organ (as sight is the act of the eye), but not because the process of human knowing does not involve any material operation whatsoever. The brain, as a material organ, obviously plays some pivotal role. The intellect, though, cannot be the act of the brain because the operation of the intellect, although it has recourse to that which is taken from sensation, cannot possibly be reduced to anything material.

    Your final question raises an interesting point. We can, in fact, use the idea that the intellect knows the brain as an argument for its immateriality. Why is the human intellect able to know the brain? I would say that it can do so because the brain is a sensible body. As a sensible body, the intellect is able to know it because the human intellect is able to know all sensible bodies as such. In other words, the intellect is receptive of all sensible natures in the same way that the eye is receptive of color or the ear is receptive of sound. In order to operate in such a manner, the intellect must not itself be the act of a bodily organ. This is because, in order for the eye to receive color, for example, it must itself lack color. That which is able to receive something cannot already possess that which it is able to receive. If the eye, of itself, always was in the possession of some color then it would simply be unable to see other colors. In the same way, the human intellect could not be receptive of all things sensible if it was itself a sensible organ. In order to know bodily things as such it must not itself be bodily.