The only roads of enquiry there are to think of: one, that it is and that it is not possible for it not to be, this is the path of persuasion (for truth is its companion); the other, that it is not and that it must not be - this I say to you is a path wholly unknowable.
ParmenidesNever will this prevail, that the things that are not are — bar your thought from this road of inquiry.
ParmenidesYou must learn all things, both the unshaken heart of persuasive truth, and the opinions of mortals in which there is no true warranty.
ParmenidesWe can speak and think only of what exists. And what exists is uncreated and imperishable for it is whole and unchanging and complete. It was not or nor shall be different since it is now, all at once, one and continuous.
Parmenides