It will contribute towards one's object, who wishes to acquire a facility in the gaining of knowledge, to doubt judiciously.

For even they who compose treatises of medicine or natural philosophy in verse are denominated Poets: yet Homer and Empedocles have nothing in common except their metre; the former, therefore, justly merits the name of the Poet; while the other should rather be called a Physiologist than a Poet.

Xenophanes states that the fire in Lipara once failed for sixteen years, but returned in the seventeenth year. They say that the lava-stream in Etna is neither flaming nor continuous, but returns only after an interval of many years.

Now the soul of man is divided into two parts, one of which has a rational principle in itself, and the other, not having a rational principle in itself, is able to obey such a principle. And we call a man in any way good because he has the virtues of these two parts.

The hardest victory is the victory over self.

And of course, the brain is not responsible for any of the sensations at all. The correct view is that the seat and source of sensation is the region of the heart.

No excellent soul is exempt from a mixture of madness.