And if again we consider that among the supposed forty-three millions each variety would have its counter type or complementary individual, then we realize the enormous number of perfect unions which would be theoretically possible, and the enormous number of distinct and different ways in which the race-life could thus find adequate and admirable expression for itself. However, we are here getting into a somewhat abstract region. To return to the practical, the complementary idea certainly seems to account for much of human union; for though there are but few cases in which the qualities of the uniting parties are really quite complementary to each other, yet it is obvious that each person tends to seek and admire attributes in the other which he himself possesses only in small degree. At the same time, it must not be forgotten that _some_ common qualities and common ground are necessary as a basis for affection, and that sympathy and agreement in like interests and habits are at least as powerful a bond as admiration of opposites. It sometimes happens that there are immense romances between people of quite different classes and habits of life, or of quite different race and color; and they see, for the moment, flaming ideals and wonder-worlds in each other. But unions in such cases are doubtful and dangerous, because so often the common ground of sympathy and mutual understanding will be too limited; and hereditary instincts and influences, deep-lying and deep-working, will call the wanderers away, even from the star which they seek to follow. Sympathy with and understanding of the person one lives with must be cultivated to the last degree possible, because it is a condition of any real and permanent alliance. And it may even go so far (and should go so far) as a frank understanding and tolerance of such person’s _other_ loves. After all, it seldom happens, with any one who has more than one or two great interests in life, that he finds a mate who can sympathize with or understand them all. In that case a certain portion of his personality is left out in the cold, as it were; and if this is an important portion it seems perfectly natural for him to seek for a mate or a lover on that side too. Two such loves are often perfectly compatible and reconcilable—though naturally one will be the dominant love, and the other subsidiary, and if such secondary loves are good-humoredly tolerated and admitted, the effect will generally be to confirm the first and original alliance all the more.