Aristotle on the Common Sense

The following is an article (very lightly edited here) that I wrote and put on the Internet in 2009. I wrote it while reading the book Aristotle on the Common Sense. I later wrote a review of the book for Amazon here. 

The book's introduction outlines the basic issue. Plato gives his position in his dialogue Thaeatetus. Each kind of sense -- vision, touch, taste, hearing, smell -- is autonomous. Something contains the senses, but cannot use them. Having the senses and being able to use them is another part of being an animal, which includes other capacities and a suitable body. To perceive by means of the eyes suggests there is a subject that uses the sense of sight localized in the eyes. Plato calls this subject 'soul', where each of the senses converge. The soul can integrate the senses and use the result. The soul uses the senses primarily to receive impressions of the basic sensory qualities. Also, the soul applies 'sameness' and 'difference' to sensory qualities. Such coordination of the senses seems to involve thinking. In Plato's view the senses are not integrated at the level of perception, but at the level of thought. It is compatible with Plato's wider philosophy to dissociate knowledge from perception.

When later Aristotle considers perception, he tries to give an account of nonhuman animals as well. The often very complex behavior of animals might be explained on Plato's framework, provided one attributes some level of thought to nonhuman animals. It seems Aristotle would not, that his position was that nonhuman animals cannot think or form opinions. An animal's survival depends on the ability to differentiate and associate sensible qualities (e.g. cold and hard versus soft and warm, smell and taste). The animal seems to apply 'same' and 'different' to them. Aristotle agreed with Plato that integration occurs and the subject is able to use the result, but he disagreed about where or how. Per Aristotle the senses are not integrated at the same level as thinking, but by what he calls the 'common sense'. He wrote very little about it, but held such integration to be perceptual. It could thus be attributed to nonhuman animals.

An interesting aside is where each philosopher believed sensory integration to occur. Plato thought it was the brain, where he believed the rational soul was (in his dialogue Timaeus). Aristotle located the common sense to be in the heart. We can discount both views given the paucity of knowledge about anatomy when they lived, but it is fascinating to see Aristotle rationalize his position.

According to Aristotle the 'common sensibles', or 'common perceptibles', are motion, rest, shape, magnitude, number, and unity (De Anima III.1 425a16). (Different translations might use slightly different terms here.) Common perceptibles are those apprehended by more than one sense. For example, extension is perceived by both touch and sight. Would the reader consider time a common perceptible? What Aristotle called the 'special perceptibles' were those attributable to one sense only, e.g. warmth, color, taste, smell and sound.

This concludes my presenting the views of Plato and Aristotle. What does Ayn Rand say about this? It did not surprise me that her view better aligns with Aristotle. However, she said so little about it. "A percept is a group of sensations automatically retained and integrated by the brain of a living organism. It is in the form of percepts that man grasps the evidence of his senses and apprehends reality" (ITOE2, p. 5). "Similarity is grasped perceptually" (p. 14). That is about all -- various sensory data is automatically integrated into percepts. Her published works barely reach beyond that. We could add that her view of thinking and consciousness being under volitional control buttresses her view that perceptual integration is automatic.

To some extent our sensory apparatus is under volitional control. For example, we can choose where to look or direct our attention to specific sounds. This, of course, raises the question of volition in nonhuman animals, a topic on which I venture no further here.

To conclude I present this short essay as food for thought. Often in philosophy more questions are raised than can be answered. This is a hazard of philosophy. On the other hand, such food is the nourishment of the soul.