(from Greek entelecheia), in philosophy, that which realizes or makes actual what is otherwise merely potential. The concept is intimately connected with Aristotle's distinction between matter and form, or the potential and the actual. He analyzed each thing into the stuff or elements of which it is composed and the form which makes it what it is (see hylomorphism). The mere stuff or matter is not yet the real thing; it needs a certain form or essence or function to complete it. Matter and form, however, are never separated; they can only be distinguished. Thus, in the case of a living organism, for example, the sheer matter of the organism (viewed only as a synthesis of inorganic substances) can be distinguished from a certain form or function or inner activity, without which it would not be a living organism at all; and this “soul” or “vital function” is what Aristotle in his De anima (On the Soul ) called the entelechy (or first entelechy) of the living organism. Similarly, rational activity is what makes a man to be a man and distinguishes him from a brute animal.

Gottfried Wilhelm Leibniz (Leibniz, Gottfried Wilhelm), a 17th-century German philosopher and mathematician, called his monads (the ultimate reality of material beings) entelechies in virtue of their inner self-determined activity. The term was revived around the turn of the 20th century by Hans Driesch, a German biologist and philosopher, in connection with his vitalistic biology to denote an internal perfecting principle which, he supposed, exists in all living organisms.