X. comes, let us say, from a family in which there is a persistent taint of epilepsy, or insanity. X. is a normal, useful, conscientious member of society. To talk of segregating such an individual would be rash. But X. has given some thought to heredity and eugenics, and decides that he, or she, will refrain from marriage, in order to avoid transmitting the family taint to another generation. Here we have, in effect, a non-coercive restriction of reproduction. What shall we say of the action of X. in remaining celibate,--is it wise or unwise? To be encouraged or condemned? It is perhaps the most delicate problem which applied eugenics offers. It is a peculiarly personal one, and the outsider who advises in such a case is assuming a heavy responsibility, not only in regard to the future welfare of the race, but to the individual happiness of X. We can not accept the sweeping generalization sometimes made that "Strength should marry weakness and weakness marry strength." No more can we hold fast to the ideal, which we believe to be utopian, that "Strength should only marry strength." There are cases where such glittering generalities are futile; where the race and the individual would both be gainers by a marriage which produced children that had the family taint, but either latent or not to a degree serious enough to counteract their value. The individual must decide for himself with especial reference to the trait in question and his other compensating qualities; but he should at least have the benefit of whatever light genetics can offer him, before he makes his decision. For the sake of a concrete example, let us suppose that a man, in whose ancestry tuberculosis has appeared for several generations, is contemplating marriage. The first thing to be remembered is that if he marries a woman with a similar family history, their children will have a double inheritance of the taint, and are almost certain to be affected unless living in an especially favorable region. It would _in most cases_ be best that no children result from such a marriage.