I. Pain and pleasure are produced in men's minds by the action of certain causes. But the quantity of pleasure and pain runs not uniformly in proportion to the cause; in other words, to the quantity of force exerted by such cause. The truth of this observation rests not upon any metaphysical nicety in the import given to the terms cause, quantity, and force: it will be equally true in whatsoever manner such force be measured.
II. The disposition which any one has to feel such or such a quantity of pleasure or pain, upon the application of a cause of given force, is what we term the degree or quantum of his sensibility. This may be either general referring to the sum of the causes that act upon him during a given period: or particular, referring to the action of any one particular cause, or sort of cause.
III. But in the same mind such and such causes of pain or pleasure will produce more pain or pleasure than such or such other causes of pain or pleasure: and this proportion will in different minds be different. The disposition which any one has to have the proportion in which he is affected by two such causes, different from that in which another man is affected by the same two causes, may be termed the quality or bias of his sensibility. One man, for instance, may be most affected by the pleasures of the taste; another by those of the ear. So also, if there be a difference in the nature or proportion of two pains or pleasures which they respectively experience from the same cause; a case not so frequent as the former. From the same injury, for instance, one man may feel the same quantity of grief and resentment together as another man: but one of them shall feel a greater share of grief than of resentment: the other, a greater share of resentment than of grief.
IV. Any incident which serves as a cause, either of pleasure or of pain, may be termed an exciting cause: if of pleasure, a pleasurable cause: if of pain, a painful, afflictive, or dolorific cause.
V. Now the quantity of pleasure, or of pain, which a man is liable to experience upon the application of an exciting cause, since they will not depend altogether upon that cause, will depend in some measure upon some other circumstance or circumstances: these circumstances, whatsoever they be, maybe termed circumstances influencing sensibility.
VI. These circumstances will apply differently to different exciting causes; insomuch that to a certain exciting cause, a certain circumstance shall not apply at all, which shall apply with great force to another exciting cause. But without entering for the present into these distinctions, it may be of use to sum up all the circumstances which can be found to influence the effect of any exciting cause. These, as on a former occasion, it may be as well first to sum up together in the concisest manner possible, and afterwards to allot a few words to the separate explanation of each article. They seem to be as follows: Health. Strength. Hardiness. Bodily imperfection. Quantity and quality of knowledge. Strength of intellectual powers. Firmness of mind. Steadiness of mind. Bent of inclination. Moral sensibility. Moral biases. Religious sensibility. Religious biases. Sympathetic sensibility. Sympathetic biases. Antipathetic sensibility. Antipathetic biases Insanity. Habitual occupations. Pecuniary circumstances. Connexions in the way of sympathy. Connexions in the way of antipathy. Radical frame of body. Radical frame of mind. Sex. Age. Rank. Education. Climate. Lineage. Government. Religious profession.
VII. 1. Health is the absence of disease, and consequently of all those kinds of pain which are among the symptoms of disease. A man may be said to be in a state of health when he is not conscious of any uneasy sensations, the primary seat of which can be perceived to be anywhere in his body. In point of general sensibility, a man who is under the pressure of any bodily indisposition, or, as the phrase is, is in an ill state of health, is less sensible to the influence of any pleasurable cause, and more so to that of any afflictive one, than if he were well.