Reason transforms passions into pleasures

Animal nature, which chemists call the "animal kingdom", instinctively secures the thee means necessary to perpetuate itself. They are three real needs. It must feed itself, and in order that doing so shall not be a labor, it has the sensation called 'appetite'; and it finds pleasure in satisfying it. In the second place it must preserve its own species by generation, and certainly it would not perform that duty - despite what St. Augustine says - if it did not find pleasure in doing it. In the third place it has an unconquerable inclination to destroy its enemy; and nothing is better contrived, for since it must preserve itself it must hate whatever achieves or desire it's destruction. Under this general law, however, each species acts independently. These three sensations - hunger, appetite for coitus, hate which tend to destroy the enemy - are habitual satisfactions in brute beasts, let us not call them pleasure, for, endowed with the faculty of reason, he foresees it, seeks it, creates it, and reasons about it after enjoying it. Let us examine the thing. Man is in the same condition as the beast when he yields to these three instincts without his reason entering in. When our mind makes its contribution, these three satisfactions become pleasure, pleasure, pleasure: the inexplicabile sensation which makes us taste what we call happiness, which we cannot explain either, although we feel it.

The voluptuary who who reasons disdain greediness, lust, and the brutal vengeance which springs from a first impulse of anger; he is an epicure; he falls in love but he does not wish to enjoy the object he loves unless he is sure that he is loved; when he is insulted, he will not avenge himself untill he has coldly arrived at the best way to relish the pleasure of his revenge. In the result he is more cruel, but he consoles himself by the knowledge that he is at least reasonable. These three operations are the work of the soul, which, to procure itself pleasure, becomes the minister of the passion. We beat hunger in order to savour culinary concoction better; we put off the pleasure of love in order to make it more intense; and we defer a vengeance in order to make it more deadly. Yet it is true that people often die of indigestion, that we deceive ourselves or allow ourselves to be deceived in love by sophisms, and that the object we wish to exterminate often escapes our vengeance; but we run these risks willingly.

Giacomo Casanova - The history of my life (4, 2)