 Cartesian dualism is, of course, traditionally associated with the view that animals lack minds. Descartes' argument for this view was not based, however, on any ontological principles, but upon what he took to be the failure of animals to use language rationally, or to reason generally. On this basis he claimed that nothing in animal behavior requires a non-mechanistic, mental explanation; hence he saw no reason to attribute possession of mind to animals.  In a sense, therefore, the Cartesian argument for the human-uniqueness of consciousness rests on the premise that material processes are insufficient to account for human capacities for language, rationality, and self-awareness (i.e. the awareness of oneself as, putatively, an essentially thinking thing) — and hence a non-material soul was posited to account for these phenomena.  Few today would hold that material processes are incapable of producing complex phenomena such as language and rationality, and indeed our understanding of ‘the material’ has changed dramatically since Descartes' time. However, the subjective nature of consciousness continues to motivate some authors to argue that mental phenomena cannot be reduced to physical phenomena.