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.