Chapter 17.—The Nature of Error. All Error is Not Hurtful, Though It is Man’s Duty as Far as Possible to Avoid It. For although we ought with the greatest possible care to avoid error, not only in great but even in little things, and although we cannot err except through ignorance, it does not follow that, if a man is ignorant of a thing, he must forthwith fall into error. That is rather the fate of the man who thinks he knows what he does not know. For he accepts what is false as if it were true, and that is the essence of error. But it is a point of very great importance what the subject is in regard to which a man makes a mistake. For on one and the same subject we rightly prefer an instructed man to an ignorant one, and a man who is not in error to one who is. In the case of different subjects, however,—that is, when one man knows one thing, and another a different thing, and when what the former knows is useful, and what the latter knows is not so useful, or is actually hurtful,—who would not, in regard to the things the latter knows, prefer the ignorance of the former to the knowledge of the latter? For there are points on which ignorance is better than knowledge. And in the same way, it has sometimes been an advantage to depart from the right way,—in travelling, however, not in morals. It has happened to myself to take the wrong road where two ways met, so that I did not pass by the place where an armed band of Donatists lay in wait for me. Yet I arrived at the place whither I was bent, though by a roundabout route; and when I heard of the ambush, I congratulated myself on my mistake, and gave thanks to God for it. Now, who would not rather be the traveller who made a mistake like this, than the highwayman who made no mistake? And hence, perhaps, it is that the prince of poets puts these words into the mouth of a lover in misery: 1111 “How I am undone, how I have been carried away by an evil error!” for there is an error which is good, as it not merely does no harm, but produces some actual advantage. But when we look more closely into the nature of truth, and consider that to err is just to take the false for the true, and the true for the false, or to hold what is certain as uncertain, and what is uncertain as certain, and that error in the soul is hideous and repulsive just in proportion as it appears fair and plausible when we utter it, or assent to it, saying, “Yea, yea; Nay, nay,”—surely this life that we live is wretched indeed, if only on this account, that sometimes, in order to preserve it, it is necessary to fall into error. God forbid that such should be that other life, where truth itself is the life of the soul, where no one deceives, and no one is deceived. But here men deceive and are deceived, and they are more to be pitied when they lead others astray than when they are themselves led astray by putting trust in liars. Yet so much does a rational soul shrink from what is false, and so earnestly does it struggle against error, that even those who love to deceive are most unwilling to be deceived. For the liar does not think that he errs, but that he leads another who trusts him into error. And certainly he does not err in regard to the matter about which he lies, if he himself knows the truth; but he is deceived in this, that he thinks his lie does him no harm, whereas every sin is more hurtful to the sinner than to the sinned against. 1111     Virgil, Eclog . viii. 41.