Impact of Parmenide's Concept of Constant Being and Heraclitu's Concept of Changeable and Inconstant Being on Plato's Ontology

Doubtlessly, future is the result of past. So, it may be said that all scientific and philosophical theories are resulted from thinking on theories, concepts and issues of earlier thinkers. Parmenides and Heraclitus are two important pre-Socratic philosophers who had two contradictory attitudes towards being. This essay claims that founding his theory of intelligible (ideas) and sensible worlds, Plato used Parmenides’ concept of constant being and Heraclitu's concept of changeable and inconstant being. Comparing their statements, this paper has tried to show how Parmenides’ concept of being has been incorporated into Plato’s theory of Ideas. Moreover, I explained that although Plato accepted some Parmenidean elements of thought, being inspired by his predecessor, Heraclitus who rejected Parmenide's view on sensible world and proposed a novel view and tried to answer to the criticisms which may be raised about his theory of sensible and intelligible worlds and their relations.