Abstract

DESCARTES was a dualist and Spinoza a monist. If this marks a contrast between them, there ought to be a question to which Descartes’s answer was “two” and Spinoza’s “one”. (a) How many substances are there? Spinoza: “One.” Descartes: “Strictly speaking, one; but if we relax the criteria for substantiality a little, millions.” On no interpretation of the question did Descartes answer, “Two.” (b) How many basic kinds of substance are there? Descartes: “Two.” Spinoza: “Two; though there is only one substance, and it is of both kinds.” Descartes is usually called a dualist because he took thought and extension to be the two basic, logically independent ways of being; but in this sense Spinoza was a dualist, too. If we take seriously his talk of “infinite” attributes, we may call him a pluralist on this point, but certainly not a monist. (c) Of how many substances does an embodied person consist? Descartes (ignoring his views about the divisibility of matter): “Two: an embodied person is made up of a body and a mind, which are distinct substances.” Spinoza: “None: an embodied person is a mode (under two attributes) of the one and only substance, and is not made up of any number of substances.” Those are the questions which come most readily to mind, and none yields a dualist/monist contrast between Descartes and Spinoza. But: (d) Given that A and B are basic, logically independent attributes, what is the smallest number of substances needed to instantiate both A and B? To this Descartes does answer “Two” and Spinoza does answer “One.” I suspect that those who “contrast” Descartes and Spinoza as dualist and monist usually have in mind not the genuine contrast brought out by (d) but rather the fact that Descartes answered “Two” to (b) while Spinoza answered “One” to (a). Still, (d) is important in the thinking of both philosophers and in the philosophy of mind generally. Strawson's chapter, “Persons,” for example, is interesting partly for its Spinozist answer to (d): Strawson does not reduce mental predicates to physical or vice versa, but says that predicates of both kinds may apply to a single thing, namely a person..