ananke (Greek), necessity. The term was used by early Greek philosophers for a constraining or moving natural force. In Parmenides (frg. 8, line 30) ananke encompasses reality in limiting bonds; according to Diogenes Laertius, Democritus calls the vortex that generates the cosmos ananke; Plato (Timaeus 47e ff.) refers to ananke as the irrational element in nature, which reason orders in creating the physical world. As used by Aristotle (Metaphysics V.5), the basic meaning of ‘necessary’ is ‘that which cannot be otherwise’, a sense that includes logical necessity. He also distinguishes (Physics II.9) between simple and hypothetical necessity (conditions that must hold if something is to occur). See also ARIS- TOTLE , PARMENIDE. W.J.P.