Parmenides Quote

You must learn all things, both the unshaken heart of persuasive truth, and the opinions of mortals in which there is no true warranty.

Frag B 1.28-30, quoted by Sextus Empiricus, Against the Mathematicians, vii. 3; Simplicius, Commentary on the Heavens, 557-8; Proclus, Commentary on the Timaeus I, 345