Accordingly in this paper I address those only who are drawn to teaching by the love of it, who regard it as the most vital of the Fine Arts, who intend to give their lives to mastering its subtleties, and who are ready to meet some hardships and to put up with moderate fare if they may win its rich opportunities. But supposing such a temper, what special qualifications will the work require? The question asked thus broadly admits no precise answer; for in reality there is no human excellence which is not useful for us teachers. No good quality can be thought of which we can afford to drop. Some day we shall discover a disturbing vacuum in the spot which it left. But I propose a more limited problem: what are those characteristics of the teacher without which he must fail, and what those which, once his, will almost certainly insure him success? Are there any such essentials, and how many? On this matter I have pondered long; for, teaching thirty-nine years in Harvard College, I have each year found out a little more fully my own incompetence. I have thus been forced to ask myself the double question, through what lacks do I fail, and in what direction lie the roots of my small successes? Of late years I think I have hit on these roots of success and have come to believe that there are four of them,--four characteristics which every teacher must possess. Of course he may possess as many more as he likes,--indeed, the more the better. But these four appear fundamental. I will briefly name them. First, a teacher must have an aptitude for vicariousness; and second, an already accumulated wealth; and third, an ability to invigorate life through knowledge; and fourth, a readiness to be forgotten. Having these, any teacher is secure. Lacking them, lacking even one, he is liable to serious failure. But as here stated they have a curiously cabalistic sound and show little relation to the needs of any profession. They have been stated with too much condensation, and have become unintelligible through being too exact. Let me repair the error by successively expanding them.