The act of sympathy follows the general law that nature works onward by mixing like and unlike, continuity and change; and so illustrates the same principle that we see in the mingling of heredity with variation, specific resemblance with a differentiation of sexes and of individuals, tradition with discussion, inherited social position with competition, and so on. The likeness in the communicating persons is necessary for comprehension, the difference for interest. We cannot feel strongly toward the totally unlike because it is unimaginable, unrealizable; nor yet toward the wholly like because it is stale—identity must always be dull company. The power of other natures over us lies in a stimulating difference which causes excitement and opens communication, in ideas similar to our own but not identical, in states of mind attainable but not actual. If one has energy he soon wearies of any habitual round of activities and feelings, and his organism, competent to a larger life, suffers pains of excess and want at the same time. The key to the situation is another person who can start a new circle of activities and give the faculties concerned with the old a chance to rest. As Emerson has remarked, we come into society to be played upon. “Friendship,” he says again, “requires that rare mean betwixt likeness and unlikeness, that piques each with the presence of power and of consent in the other party.... Let him not cease an instant to be himself. The only joy I have in his being mine is that the _not mine_ is _mine_.... There must be very two before there can be very one.”[31] So Goethe, speaking of Spinoza’s attraction for him, remarks that the closest unions rest on contrast;[32] and it is well known that such a contrast was the basis of his union with Schiller, “whose character and life,” he says, “were in complete contrast to my own.”[33] Of course, some sorts of sympathy are especially active in their tendency, like the sympathy of vigorous boys with soldiers and sea-captains; while others are comparatively quiet, like those of old people renewing common memories. It is vivid and elastic where the tendency to growth is strong, reaching out toward the new, the onward, the mysterious; while old persons, the under-vitalized and the relaxed or wearied prefer a mild sociability, a comfortable companionship in habit; but even with the latter there must always be a stimulus given, something new suggested or something forgotten recalled, not merely a resemblance of thought but a “resembling difference.” And sympathy between man and woman, while it is very much complicated with the special instinct of sex, draws its life from this same mixture of mental likeness and difference. The love of the sexes is above all a need, a need of new life which only the other can unlock. “Ich musst’ ihn lieben, weil mit ihm mein Leben Zum Leben ward, wie ich es nie gekannt,”[34]