  For many commentators, Gassendi's empiricist theory of knowledge and objections to Descartes's Meditations count as his paramount philosophical contributions. In his core epistemology, he offers the first modern model of knowledge from the senses to be integrated with a physiological account of perception. In his objections to Descartes, he rejects the clarity and distinctness criterion, seeks to undermine the reasoning behind the cogito, and assails the ontological argument. Each of these views represents a battle Gassendi has taken up against the Aristotelian tradition or the Cartesian stance; his thoroughgoing empiricism poses an alternative to both of these competing perspectives.