After what we have just said, it is clear that love is derived from two factors: (1) _momentary sexual passion_; (2) _the hereditary and instinctive sentiments of sympathy which are derived from the primordial sexual appetite of our animal ancestors, but which have become completely independent of this appetite_. Between these two terms are placed the sentiments of sympathy experienced by the individual in his former life, which have most often been provoked by sexual desire for an individual of the opposite sex, and which may be evoked by the aid of remembrance, kindled afresh, and contribute strongly to maintain constancy of love. These different sentiments pass into each other in all possible shades, and continually react on each other. Sexual appetite, for example, awakens sympathy, and is awakened by the latter in its turn; on the contrary, it is cooled or extinguished under the influence of bad conduct on the part of the person loved. Let us here recall a law of the sentiments of sympathy, a law which is well known, but generally forgotten in human calculations. Man loves best those to whom he devotes himself, and not those from whom he receives benefits.[3] It is easy to be convinced of the reality of this fact in the relations of parents to their children, as well as in marriage. When one of the conjoints in marriage adulates the other, the latter may easily find this adulation quite natural, and may love the other conjoint much less than a spoilt child, to which is devoted all the transports of an unreasonable affection. The spoilt child, the object of such blind affection, more often responds to it by indifference, or even by ingratitude, disdain and impertinence. We find everywhere this play of sentiments, which considerably impedes mutuality in love. It may even concern inanimate objects. We like a garden, a house or a book over which we have taken much pains, and we remain indifferent to the most beautiful and precious gifts which come by themselves without our making any effort to obtain them. In the same way, the child becomes attached to some toy which he has made himself, and disdains the costly presents given by his parents. As a poet has said: "Man only enjoys for long and without remorse the goods dearly paid for by his efforts." (Sully-Prudhomme: "_Le Bonheur_.") There is, therefore, a profound psychology in the old and wise saying that true love expresses itself as often by refusal as by compliance, and should always associate itself with reason. No doubt this is not primitive love; it is a love elevated and purified by its combination with the elements of intelligence.