entailment See IMPLICATION. entelechy (from Greek entelecheia), actuality. Aristotle, who coined both terms, treats entelecheia as a near synonym of energeia when it is used in this sense. Entelecheia figures in Aristotle’s definition of the soul as the first actuality of the natural body (On the Soul II.1). This is explained by analogy with knowledge: first actuality is to knowledge as second actuality is to the active use of knowledge. ‘Entelechy’ is also a technical term in Leibniz for the primitive active force in every monad, which is combined with primary matter, and from which the active force, vis viva, is somehow derived. The vitalist philosopher Hans Driesch used the Aristotelian term in his account of biology. Life, he held, is an entelechy; and an entelechy is a substantial entity, rather like a mind, that controls organic processes. See also ENERGEIA , PHILOSOPHY OF BIOL- OG. P.Wo.