Aristotle on Thinking

Aristotle on Thinking (Noêsis)

Copyright © 2008, S. Marc Cohen

Revised 3/8/08


The Perception Model

DA III.4-5. Aristotle gives an account of thinking (or intellect—noêsis) that is modeled on his account of perception in Book II.

Just as in perception, “that which perceives” (to aisthêtikon) takes on sensible form (without matter), so in thinking “that which thinks” (to noêtikon) takes on intelligible form (without matter).

Similarly, just as in perception, the perceiver has the quality of the object potentially, but not actually, so, too, in understanding, the intellect is potentially (although not actually) each of its objects.


This leaves us with a problem analogous to the one we considered in the case of perception. There we wondered how the perceiver of a red tomato could be potentially (but not actually) red (prior to perceiving it), and yet become red (be actually red) in the process of perceiving it.

Here the question is how the intellect that thinks about a tomato (or a horse) is potentially a tomato (or a horse), and then becomes a tomato (or a horse) in the process of thinking about it.

The problem about thinking seems more severe: for although there is a sense in which the perceiver becomes red (the sense organ becomes colored red), there does not seem to be a comparable sense in which the intellect becomes a tomato (or a horse). (1) there is no organ involved, and (2) there does not seem to be room in there for a tomato (let alone a horse).

The Differences from Perception

As we will see, there are important differences between perceiving and understanding, beyond the fact the one involves taking on perceptible form and the other intelligible form.

Perception is restricted in its objects

Not everything is perceivable. Aristotle restricts things that are perceivable intrinsically (kath’ hauta) to the proper objects of each sense and the common objects that can be perceived by more than one sense.

[p. 1]

Proper objects

The proper objects of a sense are those characteristics that are perceivable by that sense and by that sense alone (418a12-13). E.g., red and blue (and colors generally) are the proper objects of sight; sweet and sour (and flavors generally) are the proper objects of taste; sound is the proper object of hearing.

Common objects

These can be perceived by more than one sense. Aristotle lists motion, rest, number, shape, and size (418a18-20) as the common objects of the senses, since each of these can be detected by more than one sense (e.g., motion by both touch and sight).

There are also things that can be perceived only “coincidentally” (kata sumbebêkôs), such as individual substances (e.g., the son of Diares, 418a22). When you see the son of Diares, what you see intrinsically is a pale thing, which “coincides with” the son of Diares. That substance, therefore, is only coincidentally an object of perception.

Intellect is broader than perception

Intellect is not restricted in this way. Rather, “intellect understands all things” (nous panta noei, 429a19). Not only can you think about the objects of perception (colors, odors, sounds, the son of Diares, etc.), but you can think about things that can’t be perceived at all (numbers, virtues, etc.), either intrinsically or coincidentally. You can think about anything. This universality of the objects of thought has several important consequences.

Intellect is “unmixed”

The first is that the intellect “must be unmixed,” i.e., must be pure potential (since it can think about anything, it must be only potentially that thing). So it has no nature of its own—if it did, it would be unable to think about that nature.

Intellect is separable, perception is bodily

It is unreasonable for intellect to be mixed with the body, since it would then acquire some quality (for instance, hot or cold) or even, like the perceiving part, have some organ, whereas in fact it has none. (42925-27)

Since intellect does not have a bodily organ, it is separable from the body:

… intellect is separable, whereas the perceiving part requires a body. (429b5)

[p. 2]

Perception and intellect are “unaffected” in different ways (429a31-b1)

One may be deafened by a very audible noise, if it’s particularly loud. But one can’t be rendered thoughtless by something particularly intelligible. Quite the opposite, Aristotle asserts:

After a sense perceives something very perceptible, it cannot perceive; after hearing very loud sounds, for instance, it cannot hear sound …. But whenever intellect understands something that is very intelligible, it
understands more, not less, about inferior objects …. (429b4)

Intellect is reflexive in a way that perception is not

There is another important difference between perceiving and thinking that is clearly a consequence of the universality of thought—thought is capable of thinking of itself.

When the intellect becomes each thing … it is still potential in a way … and then it is capable of understanding itself. (429b6-9)

Further, intellect itself is an object of intellect in the same way is its objects are. (430a3)

This feature of intellect is what brings humans (the only animals who have intellect) as close as they come to the divine. Cf. the famous
passage in Metaphysics Λ.9 where Aristotle describes the divine intellect:

Since it is indeed the best thing, <the divine understanding> must understand itself, and its understanding is an understanding of understanding (auton ara noei, eiper esti to kratiston, kai estin hê noêsis noêseôs noêsis). (1047b34)

God’s activity, that is to say, is thinking; and the object of that thinking is just the thinking itself. God is (in Kosman’s phrase) thinking thinking thinking.

Perception is entirely passive; intellect has an “active” component

The passivity of perception seems obvious from Aristotle’s description of it as a kind of “being affected.” We do not choose to perceive; when a functioning sensory system is presented with a sensible object of the right type (e.g., functioning eyes by a patch of color), perception occurs.

But the intellect, Aristotle claims, is not entirely passive; thinking does not just happen to us—it is something we do. Cf. 430a15:

One sort of intellect corresponds to matter, by becoming all things. Another sort corresponds to the producer by producing all things ….

[p. 3]

The active (productive) intellect: Nous Poiêtikos

One of the most interesting (and challenging) parts of De Anima III is the role of nous poiêtikos. First, let us see why Aristotle thinks it is needed—why a merely passive (receptive) intellect is inadequate to account for thinking.

The Passive Intellect

Aristotle never actually uses the phrase nous pathêtikos (passive intellect), but the concept is clearly present in his account. We can reconstruct his argument as follows. It begins with the total passivity of an intellect that can “become all things.”

  1. The passive intellect is potentially each of its objects, but not actually any of them. (429a16)
  2. The passive intellect can think anything. (429a18)
  3. Hence, the passive intellect is actually nothing until it thinks. (429a23)

At this point, as J. Lear says (Aristotle: the Desire to Understand, p. 135) “there is too much potentiality around to explain how active contemplating occurs.” We can see why by reflecting on the question of how thinking is supposed to begin. What initiates thinking?

  1. The mind which can become all things—the passive intellect—is pure passive potentiality before thinking. (429a21) [It’s the cognitive counterpart of matter.]
  2. A passive potentiality requires an active counterpart. (Phys. III.3)
  3. For a potentiality to be actualized, there must be something actual as efficient cause. (431a3; cf. Met. Θ.8)
  4. Actuality is prior to potentiality. (Met. Θ.8)
  5. Hence, the passive intellect cannot be the efficient cause of its thinking.

The Active Intellect

This establishes that there is something other than the passive intellect that is the efficient cause of its thinking (i.e., of its taking on intelligible form). So what is this thing that manages to “get thought going”? The implicit argument for a new capacity looks like this:

[p. 4]

  1. It cannot be the noêton (object of thought), or we would be thinking all the time (which Aristotle knows is not so: 430a5).
  2. It cannot be the passive intellect, for that is not actual until it thinks (and at this stage in the argument, it has not yet started to think).
  3. There is thus a formal requirement for something other than either of these to play the active role. So, there is an active intellect (nous poiêtikos).

What is the active intellect, and what does it do?

These are two of the most vexing questions of Aristotelian scholarship. Answering the second question is the key to having any hope of answering the first.

The Analogy with Light

The best place to begin is with the analogy Aristotle draws between the role of the active intellect in thinking with the role of light in perception.

Another sort <of intellect> corresponds to the producer by producing all things in the way that a state, such as light, produces things—for in a way light makes potential colors into actual colors (430a16-18).

An aisthêton (object of perception), such as color, and a functioning
aisthêterion (sense organ), such as the eye, are not sufficient for perception to occur. We also need a medium to connect the aisthêton
to the aisthêterion, to connect the color to the eye.

The medium for vision is transparent (air, water), and must be active. I.e., there must be light, which is by definition active: it is the actuality of the transparent (medium) qua transparent (II.7). “Light makes potential colors actual colors” (430a17). This means we should have a pattern in thought that mirrors the one we have in perception:

| Perception | Thought |
| aisthêton (color) | noêton |
| receptive organ (eye) | the passive intellect |
| medium in an active state (light) | the active intellect |

[p. 5]

The active intellect thus does something analogous to making potential colors actual colors. But we must now take into account the grades of actuality and potentiality. To make something actual is to raise it to either a first or a second actuality. The question is (where V is some verb of action) whether “making actual” means “making V-able” (actuality1) or “making V-ed” (actuality2)?

The question about light: does light make something actually
visible (actuality1), or actually seen (actuality2)?

The question about thought: does the active intellect make something
actually thinkable (actuality1), or actually thought (actuality2)?

Here the analogy between perception and thought seems to break down. Because whereas we’d like to say that the active intellect makes the merely thinkable into something actually2 thought about, it seems that light merely makes things visible (actuality1), but is not sufficient to make them actually2 seen.

Kosman (“What does the Maker Mind Make?”) suggests a way out. if we look again at the light analogy, we see that light can be correctly described as making things visible by making them seen.

Cf. a perceiver and a colored object in a dark room. The perceiver is looking in the direction of the colored object, but in the dark it is invisible. The color is invisible until it is illuminated, at which point it becomes actually seen and thereby (at the same time) visible. That is, there is a sense in which something becomes visible (actuality1) at precisely the moment that it becomes actually seen (actuality2). Similarly, the active intellect makes things thinkable by making them actually thought-about.

What is nous poiêtikos?

Answers to this question have been all over the lot: God (Zabarella), the
absolute thought of the deity (Zeller), divine intelligence separate from man (Alexander of Aphrodisias). These interpretations obviously lean on the connection between the discussion in DA III.4-5 and that in Metaph. Λ.9.

[p. 6]

I am inclined toward a more deflationary interpretation—nous poiêtikos is merely the capacity to initiate thought, but is not a substance. Aristotle’s somewhat substantial way of talking about it is misleading in this respect. And the fact that it is God’s most distinctive characteristic does not make it exclusively divine.

Nous poiêtikos is thus not “a mind” but an aspect of the mind; an aspect of a person’s mental capacities. The characteristics that have led some to identify nous poiêtikos with God or with something divine are these. It is , Aristotle says:

separate, impassive, ever-active, immortal, eternal

But these attributes can be construed more antiseptically. They are mostly features of the immateriality of nous poiêtikos. Being separate
does not imply a possible pre- or post-embodiment existence: rather,
it implies nothing more than irreducibility to anything material.

What about the immortality and eternality of the active intellect? Don’t these features imply its divinity? Not necessarily.

Immortality: It cannot “die,” for it cannot lose its potentialities: it doesn’t have any potentialities. It is not a living thing, and thus is not subject to death.

Eternality: It is eternal in the way that human intelligence is eternal
(assuming, as Aristotle would, the eternality and immutability of the
species). It is in that sense something abstract, and has the eternality of
abstract objects.

Therefore the survival of the active intellect, if indeed it survives, doesn’t amount to much. For it has no memories, no thoughts, no emotions, no personality. There cannot, therefore, be any such thing as “individual” active intellects. Your “active intellect” is not what you
really are, not your “individual essence”—it is merely your unrestricted capacity to initiate thought.

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