Of all the Pre-Socratics, Parmenides and the Atomists were the least understandable to me. Parmenides, unlike the Milesians, and Atomists, unlike Empedocles and Anaxagoras, took me much more time than I expected before to get a clear vision of their philosophy. But only now I have understood that Parmenides’ ideas are actually the simplest to grasp of all of them. Simple is genius.
Parmenides has built the most logical cosmogonical system of all the others, proposed by philosophers before Socrates, with the exception of the philosophy of the Atomists, which was actually the answer to that of Parmenides. But for now I will consider only those, I have already written about – Thales, Anaximander, Anaximenes, and Heraclitus.
Thales stated that everything is water. Anaximander thought that everything is Apeiron (indefinite). Anaximenes said that everything is air. Heraclitus’ fire stands alone, and I will explain below why. Parmenides had objected to all the Milesians that if there is no many, but one substance, then there must be of it as much in one place as in another, which makes impossible the assumption that everything is one substance in a particular state.
Heraclitus is a bit different story. He regarded fire as the representation of continious flux. “Everything, like flame in a fire, is born by the death of something else.” So, Heraclitus thought that everything is constantly changing. Parmenides retored that change is impossible. He argued that “what is – is, what is not – is not”, and therefore Nothing does not exist. If Nothing does not exist, then there is no past and future, because the One (our world) would have to come from Nothing, if there was past, and it would have to go into Nothing, if there was future. If there is no past and future, there is no change.
Also, Heraclitus held that motion is produced by the mingling of opposites. Parmenides thought there were no opposites, and said that “hot” is “not cold”, and “dark” is “not light”.
So, unlike previous philosophers, Parmenides based his metaphysics purely on logic. This is his Way of Truth, which can only be reached by pure reason. Russell: “He is often said to have invented logic, but what he really invented was metaphysics based on logic.