Daniel Gill

“Parmenides was offering a rational deduction. He starts from a basic principle—that you can have “is,” but you can’t have “is not”—and then proceeds to explore the consequences, whatever they might be. Whatever we make of his argument, this is a real quantum leap in the history of philosophy. Parmenides is not just offering explanations of what he can see around him, though he goes on to do that in the way of opinion. Rather, he puts all his trust in reason itself, and trusts the power of argument more than he trusts the evidence of his own eyes and ears. This is not to say that Parmenides is the first Pre-Socratic to offer arguments. Already with Thales, I suggested that he may have had implicit arguments for his views on water and the claim that everything is full of gods. Nonetheless Parmenides does represent something new. He tries to settle an abstract philosophical issue—the nature of being itself—with an explicit and complex deductive argument.”
― Peter Adamson, Classical Philosophy