He also used to say that philosophy was of a twofold character; one kind resting on certain truth, the other on opinion. On which account he says some where:
And ’twill be needful for you well to know,
The fearless heart of all-convincing truth:
Also the opinions, though less sure, of men,
Which rest upon no certain evidence.
III. Parmenides too philosophizes in his poems; as Hesiod and Xenophanes, and Empedocles used to. And he used to say that argument was the test of truth; and that the sensations were not trustworthy witnesses. Accordingly, he says:—
Let not the common usages of men
Persuade your better taught experience,
To trust to men’s unsafe deceitful sight,
Or treacherous ears, or random speaking tongue: