A habit never fails to admonish us of the wonted time of gratification, by raising a pain for want of the object, and a desire to have it. The pain of want is always first felt; the desire naturally follows; and upon presenting the object, both vanish instantaneously. Thus a man accustomed to tobacco, feels, at the end of the usual interval, a confused pain of want, which in its first appearance points at nothing in particular, though it soon settles upon its accustomed object. The same may be observed in persons addicted to drinking, who are often in an uneasy restless state before they think of their bottle. In pleasures indulged regularly and at equal intervals, the appetite, remarkably obsequious to custom, returns regularly with the usual time of gratification; and a sight of the object in the interim, has scarce any power to move it. This pain of want arising from habit, seems directly opposite to that of satiety. Singular it must appear, that frequency of gratification should produce effects so opposite as are the pains of excess and of want.
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.