Unmixing the Intellect:
Aristotle on Cognitive Powers and Bodily Organs

by Joseph Magee

Aristotle, in De Anima, Book III, Chapter 4 offers what appears to be, and what traditionally has been taken to be, demonstrations that the intellect is spatially separate or separable from the body. The chapter, however, is frustratingly cryptic and elliptical, for Aristotle leaves many of his key terms undefined and key premisses unstated. Because of the difficulty the chapter poses for interpretation and evaluation, some Aristotelian scholars claim that the traditional interpretation, or any interpretation which makes nous, i.e. mind or intellect, spatially separate, is fundamentally mistaken. These scholars instead see Aristotle's account of nous as completely consistent with what they see as his overall materialist account of soul. According to Michael Wedin, for example, Aristotle’s assertions that nous is unmixed are offered merely as support for the contention that the mind is nothing actual until it thinks.(1) Drawing on a cognitivist conception of mental states, Wedin argues that receptive mind, while having no specific physical organ, nevertheless depends on a set of bodily structures, and is realized in these bodily structures as a higher-level functional organization of the person. Thus, according to Wedin, mind as described in DA 3.4 is not spatially separable, but separable only in thought (429a10). Before evaluating the validity of any argument for the conclusion that nous is separate from the body, one must first consider Wedin’s view that Aristotle does not intend to prove this conclusion in DA 3. 4.

Despite the misgivings of Wedin, Aristotle nevertheless seems to offer three arguments that nous is a non-bodily power. In the conclusions of these arguments, he describes it as unmixed (429a18; 24) or as separate from the body (429b6; 22). In all of the arguments, he seems to justify his conclusions by at once asserting that nous and sense are similar in their cognitive activity, and yet that the activity of the senses has certain characteristic features on account of their organs. Since nous does not have these characteristics, Aristotle concludes that it is not a power whose activity is realized in any bodily organ. In the first argument, Aristotle states that, presumably because the bodily organs in which sensation occurs restrict the range of objects of the senses, the fact that nous can know all things implies that it is unmixed with the body (429a18-22). Secondly, the senses are dazzled by the intensity of their object because the intensity upsets the sense organ. However, because nous is not so dazzled, Aristotle concludes that it is separate (429b1-6). Finally, the senses know material things composed of the elements because their organs are likewise composed. Since essences are not the same as the things themselves, and since nous knows the essence of things, nous is separate from matter (429b11-22).

Despite the brevity of the summaries of these arguments, one can see that in all the arguments of DA 3. 4 Aristotle bases his conclusions on a comparison between sense and intellect. The requirements of the arguments of this chapter indicate what the nature of this analogy is. In order to prove his conclusions, Aristotle needs to compare nous and the sensitive faculty according to some feature that they share in common as cognitive powers. Moreover, this feature needs to involve bodily organs for the sense faculty so that when Aristotle specifies the differences between sensation and intellection according to this feature, he can show that the activity of nous does not likewise involve bodily organs. For, if it were supposed that nous is similar to the sensitive faculty, but in ways that for the senses did not somehow involve their organs, the differences between nous and sense would not be relevant for showing that nous has no organ.

Accordingly, Aristotle introduces DA 3. 4 with a comparison between intellection and sensation according to what seems to be at least one point of comparison relevant for demonstrating that nous is separate. He claims that the intellect is like the sense faculty in being receptive of form, and although he introduces this analogy as conditional, he presumably accepts it without argument (429a13-17). If the reception of form is a relevant point of comparison, then it needs to apply to nous as well as to the sense faculty. For, unless the reception of form applies to both nous and the senses, Aristotle would have no basis on which to conclude that nous acts without the body.(2) So, in order to accept the conclusions Aristotle claims to demonstrate about the intellect, one apparently must first accept this view of what he means by the reception of form.

Just this point, however, has recently been seriously challenged. According to Richard Sorabji, Aristotle is speaking only of a physiological change in the sense organ when he claims that sensation is the reception of form without matter.(3) Sorabji distinguishes himself from another group of interpreters, which includes Aquinas and most of the ancient commentators, who believe that the reception of form without matter describes the act of the sense faculty becoming aware of its objects.(4) Thus, the evaluation of DA 3. 4 depends upon first evaluating these claims of Sorabji. For, if Sorabji is right and nous is not like the sense faculties in being receptive of form, even though such receptivity may bear some relationship to having an organ, nevertheless, the activity of nous will imply nothing about whether nous has an organ. In evaluating Sorabji’s interpretation, it should become clear whether he is accurate in his assessment of Aquinas as well.

Next, supposing it can be shown that nous is like sense in the relevant ways, one must understand what effect having an organ has for the sensitive faculty. Since Aristotle compares the two powers in order to draw conclusions from their apparent differences, one must understand as much as possible about each term of the comparison. For instance, it seems that it is in virtue of the fact that the senses have organs which undergo some kind of physical change that Aristotle sometimes says that sensation is a kind of being affected (416b33-35).(5) Yet he also says that if sense is a sort of being acted upon and a kind of alteration, it is a special sort that should receive a special name (417a22-b22). Furthermore, he says that sense, like nous, is impassive (429a15), but that the impassivity of each is not the same (429a30). Stephen Everson has offered an interpretation of Aristotle’s perceptual theory wherein the activity of perceptual awareness supervenes on the physical and literal assimilation of sense organs to their objects.(6) Thus, the awareness of a red object comes about when and because an eye has become literally as red as the object seen. In evaluating these claims of Everson’s, it will become clear to what extent sensation is either an alteration or an activity (or both), to what extent this occurs in the physical constitution of sense organs, and what implications these facts have for sense cognition. Thus, the affectation of the sense organ, or the sense power in its organ, seems to imply certain things about the capacity of the senses. Finding a consistent interpretation of Aristotle’s theory, while difficult, is necessary for a full understanding of his distinction between sense and nous.

Finally, one must consider what specifically are the characteristics that Aristotle says distinguish nous from sense and distinguish it to the point that he can conclude that nous has no organ. If, for instance, Aristotle claims that nous knows all things, one must understand why this fact would imply that it is unmixed, that it is separate in some strong sense. Again, one must try to discover why the failure of intensely intelligible objects to dazzle nous entails that it is separate. Finally, one must see whether he can justify his conclusion that, because the essences of some things are not the same as the things themselves, the power which grasps essences is separate. If Aristotle can establish the truth of these claims, given the truth of the claims that preceded them, he will have shown that nous is unmixed and separate from the body.

The foregoing considerations should indicate with sufficient clarity the order and content of this dissertation. In the first chapter, I survey the major contemporary philosophical positions on the relation between mind and body, laying emphasis on the implications of materialist theories and their use in the development of interpretations of Aristotle’s doctrines of sense and mind. Next, in Chapter Two, I argue that DA 3. 4 was written to demonstrate that the intellect is spatially separate, and that the claims of Michael Wedin cannot stand against the overwhelming textual evidence throughout the DA supporting this conclusion. Convinced that Aristotle sought to demonstrate the separateness of the intellect, in Chapter Three I argue that Aristotle intended to claim that the intellect is like the sense faculty in being receptive of forms, against the interpretation of Richard Sorabji. In Chapter Four, I examine Aristotle’s treatment of the senses in the light of Stephen Everson’s interpretation that the act of perception supervenes on material alterations. I conclude that supervenience is incompatible with Aristotle’s account of sensation, but that, for Aristotle, the fact that the senses have organs entails certain limitations for these cognitive powers. Finally, in Chapter Five, I offer an explanation and interpretation of Aristotle’s doctrine of nous in DA 3. 4 and defend it against various alternate readings of, and objections to, Aristotle’s arguments.


1. Wedin, Michael V. "Tracking Aristotle's Nous." In Aristotle: De Anima in Focus, edited by Michael Durrant, 128-161. New York: Routledge, Inc., 1993.

2. See Jonathan Lear, Aristotle: The Desire to Understand (Cambridge: Cambridge Univresity Press, 1988), 114-115.

3. Sorabji, Richard. "Body and Soul in Aristotle." In Aristotle: De Anima in Focus, edited by Michael Durrant, 162-196. New York: Routledge, Inc., 1993. See also, "Intentionality and Physiological Precesses: Aristotle's Theory of Sense Perception." In Essays on Aristotle's De Anima, edited by Martha C. Nussbaum and Amelie Oksenberg Rorty, 195-227. Oxford: Clarendon Press, 1992.

4. Sorabji, Richard. "From Aristotle to Brentano: the Development of the Concept of Intentionality." In Festschrift for A. C. Lloyd: on the Aristotelian Tradition, edited by H. Blumenthal and H. Robinson. Oxford Studies in Ancient Philosophy, supp. vol. Oxford: Oxford University Press, 1991.

5. "So in the case of sensation, since sensation in active operation is a change of state, this must also happen. Consequently this affection persists in the sense organs, both deep down and on the surface, not only while they are perceiving but also when they have ceased to do so." De Somno, II, 459b4-7. See also De Motu Animalium 701b15-25.

6. Stephen Everson, Aristotle on Perception(Oxford: Clarendon Press, 1997).