"When, therefore, the highly lauded bliss of friendship is subjected to a true estimation, it is found to depend partly on man’s feebleness in enduring suffering, since, in fact, very strong characters are least in need of friendship, partly however in pursuing a common end; in a word, on similarity of interests, whence also the apparently more inseparable friendships are loosened or expire when on one side the dominant interests change, so that they now no longer correspond to those of the other. The pleasures attained through mutually pursued interests can, however, also only be put down to the account of these interests, not directly to that of friendship. The firmest community of interests exists in marriage; the community of goods, of earnings, of sexual intercourse, and of the education of children are strong bonds, which, in alliance with the polar completion of the spiritual qualities of both sexes, certainly suffice to found a strong and lasting friendship, which also perfectly suffices without the aid of love in the narrower sense to explain the beautiful and sublime phenomena of readiness for self-sacrifice in married life. Add to that the powerful force of habit. As the dog maintains the sublimest and most touching friendship and fidelity for his master, to whom not his own choice but chance and custom have bound him, so also the relation of spouses is essentially an alliance of habit; wherefore both mariage des convenance and love-matches after a series of years exhibit on the average the same physiognomy."