On this account, it is most appropriately denominated an oath, being the most certain sign of faith, comprehending also the testimony of God: for as he who swears, calls God to be a witness to a matter concerning which a question is raised, so it is not possible to swear so truly about any matter, as to the fact that the perfection of no art whatever can be found in the artist who professes it.

And the same assertion holds good also with respect to all the other powers which exist in us, or very nearly so; for, as they say, that no water was found in the well which had been mentioned, so also neither was there the faculty of seeing in the eyes, or that of hearing in the ears, or that of smelling in the nostrils, or, in short, any one of the senses in its corresponding organ; and similarly in the mind, there was not the faculty of comprehension.