XIX. (79) Those who investigate the nature of things as they actually exist, and who conduct their examinations of each individual matter in no negligent manner, behave very like those men who dig wells; for they also are seeking springs in an obscure place. And all men have one common desire, to find something to drink. But some men’s nature is to be nourished by the food of the soul, and that of others by the food of the body. (80) As, therefore, some of those who have dug wells have often done so without finding water; so likewise those who advance far in knowledge, and who have made great progress in it, are still often unable to attain to the end which they desire. At all events, they say that men of extensive learning often find fault with their terrible ignorance, for they only just know how far they are removed from the truth. And there is a story that some man of old time, when he was admired for his wisdom, said, that it was a fine thing that he should be admired, who only just knew that he knows nothing. (81) And choose, if you like, any art you please, whether trifling or important, and the man, too, who is most excellent, and most highly thought of in regard of his skill in it, and then consider if the professions held out by the art are equal to the performances of the artist; for if you duly examine the matter, you will find that the performance falls short of the profession, not by a small, but by a vast distance, it being almost impossible for a man to be perfect in any art whatever, which is in continual motion like a fountain, and is constantly pouring forth various species of all kinds of speculations. (82) 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. (83) 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. (84) For how could it have happened that any one should have made a mistake in what he saw, or in what he heard, or in what he understood, if the comprehensions of each of these faculties had been well established, and if they had had a trustworthy nature of themselves without God implanting accuracy in them?