Despite eschewing the utility of ends or purposes in natural philosophy, Descartes frequently engages in functional explanation, which many have assumed is an essentially teleological form of explanation. This article considers the consistency of Descartes's appeal to natural functions, advancing the idea that he is utilizing a non-normative, non-teleological form of functional explanation. It will be argued that Cartesian functional analysis resembles modern causal functional analysis, and yet, by emphasizing the interdependency of parts of biological systems, is able to avoid (...) many of the problems attendant upon modern causal theories. It is for this reason, if no other, that the study of Descartes's natural philosophy should be of interest to contemporary theorists of functional analysis. (shrink)