Parmenides and the Way of Truth

Parmenides of Elea, a Greek colony in southern Italy, wrote a philosophical poem around 475 BCE that changed the course of Greek thought. In it, a goddess teaches him two paths: the Way of Truth and the Way of Opinion. Parmenides argued that one cannot think or speak of what is not, because nothing is not there to be thought. From this he concluded that real being cannot come into existence, pass away, change or be divided, since each would require 'what is not'.

Reality must therefore be one, unchanging and complete, and the changing world of the senses is mere appearance. This conclusion is the opposite of Heraclitus' emphasis on flux. Parmenides mattered because he made reasoning, rather than sense experience, the test of truth, and he forced later thinkers such as Empedocles, the atomists and Plato to explain how change could be possible.