The appetites that respect the preservation and propagation of our species, are attended with a pain of want similar to that occasioned by habit. Hunger and thirst are uneasy sensations of want, which always precede the desire of eating or drinking: and a pain for want of carnal enjoyment precedes the desire of a proper object. The pain being thus felt independent of an object, cannot be cured but by gratification. An ordinary passion, in which desire precedes the pain of want, is in a different condition. It is never felt but while the object is in view; and therefore by removing the object out of thought, it vanisheth with its desire and pain of want[28]. These natural appetites above mentioned, differ from habit in the following particular, They have an undetermined direction toward all objects of gratification in general; whereas an habitual appetite is directed upon a particular object. The attachment we have by habit to a particular woman, differs widely from the natural passion which comprehends the whole sex; and the habitual relish for a particular dish, is far from being the same with a vague appetite for food. Notwithstanding this difference, it is still remarkable, that nature hath inforced the gratification of certain natural appetites essential to the species, by a pain of the same sort with that which habit produceth. The pain of habit is less under our power, than any other pain for want of gratification. Hunger and thirst are more easily endured, especially at first, than an unusual intermission of any habitual pleasure. We often hear persons declaring, they would forego sleep or food, rather than snuff or any other habitual trifle. We must not however conclude, that the gratification of an habitual appetite affords the same delight with the gratification of one that is natural. Far from it: the pain of want only is greater. The slow and reiterated acts that produce a habit, strengthen the mind to enjoy the habitual pleasure in greater quantity and more frequency than originally; and by this means a habit of intemperate gratification is often formed. After unbounded acts of intemperance, the habitual relish is soon restored, and the pain for want of enjoyment returns with fresh vigor.