Towards the close of the seventeenth century, however, the meaning of the term in question began to undergo a marvelous evolution, of which the end is not yet. The process was initiated by Descartes, under whose auspices psychology was changed from a science of the _soul_ into a science of the _mind_. Then, under the influence of Hume and Kant, the _noumenal mind_ disappeared, leaving only _phenomenal consciousness_. Recently, with the advent of Watson, even consciousness itself has been discarded and psychology has become a science of _behavior_. And here, for the time being, at any rate, the process has come to a stop, just one step short of complete nihilism. Woodworth quotes the following waggish comment: “First psychology lost its soul, then it lost its mind, then it lost consciousness; it still has behavior of a kind.” (“Psychology, the Science of Mental Life,” p. 2, footnote.) This gradual degeneration of psychology from animism into behaviorism is one of the greatest ironies in the history of human thought. All of this, however, was latent in the corrosive Cartesian principle of “scientific doubt.” _Facilis descensus Averni!_ It is easy to question the validity of this or that kind of human knowledge, but difficult to arrest, or even foresee, the consequences which the remorseless logic of scepticism portends. Disintegration set in, as has been said, when Descartes substituted his _psychophysical dualism_ of _mind_ and _matter_ for Aristotle’s _hylomorphic dualism_ of _soul_ and _body_. The French philosopher, in an appendix to his “Meditations,” which dates from 1670, expressly rejects the Aristotelian term of soul or _psyche_, and announces his preference for mind or spirit, in the following words: “The substance in which thought immediately resides is here called mind (mens, esprit). I here speak, however, of mens (mind) rather than anima (soul), for the latter is equivocal, being frequently applied to denote what is material” (“Reply to the Second Objections,” p. 86). Henceforth psychology ceased to be a science of the soul, and became, instead, a science of the mind.