ENTELECHY, a term used by Aristotle for that which realizes or makes actual the otherwise merely potential. The idea which is expressed by the term entelechy (EvreXixaa) is inti mately connected with Aristotle's distinction between matter and form, or the potential and actual. Briefly, one may say that he analysed each thing into the stuff or elements of which it is com posed and the form or the order in which they are arranged. The mere stuff or matter is not yet the real thing, it needs what is variously described as a certain form or essence or function to complete it ; only it must be remembered that matter and form are never separated ; they can only be distinguished. So, e.g., in the case of a living organism one may distinguish the mere matter of the organism (as though it were a mere synthesis of inorganic substances, one might almost say) from a certain form or essence or function or inner activity without which it would not really be a living organism at all ; and this "soul" or vital function, as it may be called, is what Aristotle calls the "entelechy" (or first entelechy) of a living organism. Similarly, in the case of man rational activity is what makes him really a man, as distinguished from a mere animal, and so on. Leibniz, following Aristotle, called his "monads" (or spiritual substances) entelechies, in virtue of their inner self-determined activity. And more recently the term has been revived by H. Driesch in connection with his vitalistic biology to denote an internal perfecting principle which, he sup poses, exists in all living organisms. (See ARISTOTLE, LEIBNITZ, FORM, EVOLUTION.)