Observe now, while we are, while we live, while we know that we live, while we are certain that we possess memory, understanding, and will; who boast of ourselves as having a great knowledge of our own nature; -- observe, I say, how entirely ignorant we are of what avail to us is our memory, or our understanding, or our will. A certain man who from his youth has been a friend of mine, named Simplicius, is a person of accurate and astonishing memory. I once asked him to tell me what were the last lines but one of all the books of Virgil; he immediately answered my question without the least hesitation, and with perfect accuracy. I then asked him to repeat the preceding lines; he did so. And I really believe that he could have repeated Virgil line after line backward. For wherever I wished, I made trial whether he could do it, and he did it. Similarly in prose, from any of Cicero's orations, which he had learnt by heart, he would perform a similar feat at our request, by reciting backwards as far as we wished. Upon our expressing astonishment, he called God to witness that he had no idea of this ability of his previous to that trial. So far, therefore, as memory is concerned, his mind only then learnt its own power; and such discovery would at no time be possible except by trial and experiment. Moreover, he was of course the very same man before he tried his powers; how was it, then, that he was ignorant of himself?