1. the theory that the functions of living organisms are determined, at least in part, by a life force or principle. German biologist Hans Driesch (1867–1941) was the chief exponent of this view, holding that life processes are autonomous and purposive and that potentialities for growth and development are realized through the operation of an agent to which he applied the term entelechy. French philosopher Henri Bergson (1859–1941) named this creative, vital force the élan vital.

2. more generally, any theory that opposes naturalism and the reduction of psychological life to biological structures and processes. —vitalist adj., n.