Abstract

When Descartes famously claimed that he could explain the world in terms of matter in motion, he was sounding the mantra of seventeenth century science. Though his enthusiasm about this new science has been appreciated and is well documented, the details of his contribution are viewed as riddled with paradox. These purported paradoxes revolve around Descartes's circular definition of 'motion' and 'a body', which seems to render his account of individuation implausible. ;I argue for a new interpretation of the Cartesian ontology under which these purported paradoxes, identified in Descartes's metaphysics by commentators including Kenny, Prendergast, and Garber, simply do not arise. ;In contrast to interpretations of Descartes as committed to many individual extended substances, I argue that Descartes is committed to only one individual extended substance-the whole extended universe. In my interpretation, bodies have a quasi-individual status: they acquire their individuality because the extended universe appears to perceivers as if it were divided into things like pieces of wax, stones, or birds. As quasi-individuals, bodies are also quasi-substances; this means that while they derive their materiality from the whole extended universe, they receive their individuality from human perception. I explain that the substantiality of bodies is tertiary because it involves dependence on the whole extended universe and on minds. Thus, individual bodies differ from God, who has primary substantiality because of his absolute independence, and also from the whole extended universe and minds, both of which have secondary substantiality because they are dependent solely on God. In this way, I argue that Descartes held a kind of phenomenalism about the individuation of bodies . My account is thus similar in spirit to those offered by Martial Gueroult and Thomas Lennon, though it differs sharply from both. ;I also give interpretations of clear and distinct perceptions of the real, conceptual, and modal distinctions of substances on the three levels. I show how bodies become individuated. I conclude by showing why Descartes's circular definition of motion and bodies is virtuous and not vicious