I was invited by the editor of The Encyclopedia of Philosophy to contribute this entry. I used the occasion to argue that debates about the animal mind or soul have been sensitive indicators of a number of issues in the history of modern thought: the immateriality of mind, the immortality of the soul, the existence of other minds, the basis of free will and responsibility, as well as widespread dissatisfaction with the mechanical philosophy as applied to biological and psychological phenomena. The essay is therefore, a critique of reductionism as much as it is a history of the idea. In particular, it raises the issue of the role of purposive explanation in science. It appeared in Paul Edwards, ed., The Encyclopedia of Philosophy. N.Y.: Macmillan and London: Collier-Macmillan, 1967, Vol. 1, pp. 122-27.