This account of love is not peculiar to my system, but is unavoidable on any hypothesis.  The three affections, which compose this passion, are evidently distinct, and has each of them its distinct object.  It is certain, therefore, that it is only by their relation they produce each other.  But the relation of passions is not alone sufficient.  It is likewise necessary, there should be a relation of ideas.  The beauty of one person never inspires us with love for another.  This then is a sensible proof of the double relation of impressions and ideas.  From one instance so evident as this we may form a judgment of the rest.

This may also serve in another view to illustrate what I have insisted on concerning the origin of pride and humility, love and hatred.  I have observed, that though self be the object of the first set of passions, and some other person of the second, yet these objects cannot alone be the causes of the passions; as having each of them a relation to two contrary affections, which must from the very first moment destroy each other.  Here then is the situation of the mind, as I have already described it.  It has certain organs naturally fitted to produce a passion; that passion, when produced, naturally turns the view to a certain object.  But this not being sufficient to produce the passion, there is required some other emotion, which by a double relation of impressions and ideas may set these principles in action, and bestow on them their first impulse.  This situation is still more remarkable with regard to the appetite of generation.  Sex is not only the object, but also the cause of the appetite.  We not only turn our view to it, when actuated by that appetite; but the reflecting on it suffices to excite the appetite.  But as this cause loses its force by too great frequency, it is necessary it should be quickened by some new impulse; and that impulse we find to arise from the beauty of the person; that is, from a double relation of impressions and ideas.  Since this double relation is necessary where an affection has both a distinct cause, and object, how much more so, where it has only a distinct object, without any determinate cause?

SECT.  XII OF THE LOVE AND HATRED OF ANIMALS

But to pass from the passions of love and hatred, and from their mixtures and compositions, as they appear m man, to the same affections, as they display themselves in brutes; we may observe, not only that love and hatred are common to the whole sensitive creation, but likewise that their causes, as above-explained, are of so simple a nature, that they may easily be supposed to operate on mere animals.  There is no force of reflection or penetration required.  Every thing is conducted by springs and principles, which are not peculiar to man, or any one species of animals.  The conclusion from this is obvious in favour of the foregoing system.

Love in animals, has not for its only object animals of the same species, but extends itself farther, and comprehends almost every sensible and thinking being.  A dog naturally loves a man above his own species, and very commonly meets with a return of affection.