Descartes presents his reader with many faces, among them that of an epistemologist, a mathematician, a physicist, and a physiologist, but he is best known for his distinctive metaphysical claims – for example, that he exists as a purely thinking thing, that mind and body are really distinct, that mind and body causally interact, and that God or a supremely perfect creator exists. But perceptions of Descartes’ legacy have changed repeatedly over the centuries, and the fact that he is known now primarily as a metaphysician is more reflective of us, his twenty-first-century readers, than of his own preoccupations. Recent scholarship has revealed that Descartes sees himself mainly as a scientist (or natural philosopher) who spends much of his time experimenting, studying the experiments of others, and theorizing about the results (see, e.g., Gaukroger 1995, Clarke 2006). This is in keeping with his professed view that metaphysics is something one does “once in a lifetime” (semel in vita) and that the bulk of one's intellectual life should be devoted to pursuits such as mechanics, medicine, and morality, which yield practical benefits for humankind (AT IXB 14, CSM I 186; cf. AT III 695, CSMK 228 and AT V 165). Still, Descartes believes that metaphysics is important and necessary insofar as it provides a foundation for science, and this belief is reflected in the number of pages he devotes to it in his two most important works, the Meditations and the Principles.

Descartes uses the term “metaphysics” (Latin metaphysica, French métaphysique) and its cognates infrequently in his writings, raising questions in at least one commentator's mind about whether “Cartesian thought belong[s] to metaphysics” as that term was traditionally understood by his predecessors (Marion 1999, 1–2). In his correspondence, Descartes refers to drafts of the Meditations as his “Metaphysics,” but he ultimately settles on the title Meditations on First Philosophy “because I do not confine my discussion to God and the soul, but deal in general with all the first things to be discovered by philosophizing” (AT III 235, CSMK 157). Here Descartes is assuming the Thomistic account of special metaphysics (as opposed to general metaphysics) as the science of immaterial beings, but in what follows we will use the term “metaphysics” in its broader contemporary sense, which seems very close to what he means by “first philosophy.”