It is too well known to need discussing that these things befall married couples, when their first flush of love departs and turns to coldness. The reason is that coldness in marriage occupies a higher place in the human mind than any other kind of coldness; for the principle of marriage is imprinted on the soul, in order that one soul may be propagated from another, and the father's may be continued in his children. That is why this coldness begins there and by stages spreads downwards to the following levels, where it poisons them, so turning the happiness and pleasure of the first flush of love into sadness and unpleasantness.