Descartes on Sensible Qualities

Descartes on Sensible Qualities JILL VANCE BUROKER 1. INTRODUCTION PHILOSOPHY IN THE SEVENTEENTH AND EIGHTEENTH CENTURIES can be understood in part as attempting to overthrow the Aristotelian "qualitative" physics by building a rational foundation for a new, quantitative, mechanistic physics. This project highlighted the relation between sense experience and physical reality, in order to determine the extent to which our senses provide accurate information about the world around us. Aristotle, of course, had taken for granted that the bodies we perceive actually have the colors, flavors, odors, and especially heat and cold, wet and dry we sense in them. He analyzed sensations as states of the soul, brought about by "forms" transmitted to the perceiver by the physical objects perceived, and so on his view what we sense is an exact image of a real physical property. Descartes was the first to develop a systematic account attacking this view. The qualities we sense cannot be real properties of physical objects; in fact, they are not properties of anything. For Descartes, sense qualities "exist" merely as the content of sensations, which are nothing but states of thinking substance. In Cartesian mechanics the only real physical properties, which Boyle later dubs "primary qualities,, are extension, shape, and motion. Despite the importance of this attack on sense qualities to the new physics, it is not easy to find strong support for Descartes's position in his writings. One possible basis is the oft-cited unreliability of the senses, which Descartes takes as a starting point for his method of doubt. In Discourse 4 Descartes remarks Research for this paper was made possibleby a Fellowshipfor College Teachers provided by the National Endowment for the Humanities. English versions of this paper were read at the University of Chicago, the University of Iowa, the University of Western Ontario, the University of Waterloo, the University of Southern California, the Pomona-Pitzer Philosophy Colloquium, University College, Cork, and California State University, San Bernardino. A French version was presented at the Sorbonne (Universit6 de Paris-IV) and the Universit6 de Lyons-III. I wish to thank these audiences for their comments. I am especiallyindebted to several readers for their helpful suggestions, among them Ernest Adams, Jeff King, Paul Johnson, Tom Lennon, Ed McCann,John Vickers, and Margaret Wilson, as well as two anonymous referees for theJournal. [585] 586 JOURNAL OF THE HISTORY OF PHILOSOPHY 29:4 OCTOBER 1991 that "because the senses sometimes deceive us, I decided to suppose that nothing was such as they led us to imagine."' There he cites as cases of deception the familiar examples of persons with jaundice who see everything as colored yellow, and stars or distant bodies which appear much smaller than they really are.' But even had Descartes meant to use these facts to attack the reality of sense qualities in general, they could not have supported his mechanistic physics. As Berkeley later pointed out, the unreliability of the senses casts as much doubt on the reality of size, shape, and motion as on the sense qualities Descartes wanted to banish from physical nature. A second line of attack is also fairly weak. This is the claim that extension, shape, and motion are sufficient to account for all physical phenomena. In The World Descartes says of Aristotle's four elements, hot, cold, moist, and dry: "not only these four qualities but all the others as well, including even the forms of inanimate bodies, can be explained without the need to suppose anything in their matter other than the motion, size, shape, and arrangement of its parts."~ And in Discourse 1 of The Optics he uses an analogy with the way a blind man discriminates objects by means of a stick: "You have only to consider that the differences a blind man notes between trees, rocks, water, and similar things by means of his stick do not seem any less to him than the differences between red, yellow, green, and all the other colours seem,to us. And yet in all those bodies the differences are nothing other than the various ways of moving the stick or of resisting its movements. Hence you will have reason to conclude that there is no...