Plato did not create his philosophy ex nihilo, but rather drew on four centuries of literary production in epic and lyric poetry, as well as on ethnography and historiography, tragedy and comedy, medical and mathematical research, oratory and rhetorical theory. "Words and Ideas" offers a study of Plato's philosophical language against this cultural background, retracing to their origins the history and development of the key terms of the Theory of Forms as presented in the phaedo. 'Form' or 'idea', 'essence' or 'being', 'participation', 'presence' and 'community' are among the terms investigated. The aim is to determine the precise historical and philosophical contexts on which Plato drew in the formulation of his thoughts. In tracing the roots of Plato's philosophy, "Words and Ideas" demarcates afresh Plato's position regarding the protagonists of pre-Socratic philosophy: Parmenides and the Eleatics, Anaxagoras and Diogenes of Apollonia, Leucippus and Democritus, Philolaus and the Pythagoreans.This identification of his sources allows us, in many cases for the first time, to judge what in the arguments of the dialogues is Plato's own contribution and what is there only as part of a philosophical or pre-philosophical inheritance.