The distribution, which we should be inclined to make, of our mental phenomena, according to this obvious principle, would be into those which are pleasing, those which are painful, and those which are neither painful nor pleasing. But, however obvious this first distinction may seem, as a principle of arrangement, the circumstances, on which the differences depend, are so very indefinite, that the distinction,--though it may be useful to have it in view, in its most striking and permanent cases,--cannot be adopted, as the basis of any regular system. To take the mere pleasures and pains of _sense_, for example,--to what intelligible division could we reduce these, which are not merely fugitive in themselves, but vary, from pain to pleasure, and from pleasure to pain, with a change of their external objects, so slight often, as to be scarcely appreciable, and, in many cases, even when the external objects have continued exactly the same? How small, and how variable a boundary separates the warmth which is pleasing from the heat which pains! A certain quantity of light is grateful to the eye. Increase it;--it becomes, not indifferent,--though that would be a less change,--but absolutely painful; and, if the eye be inflamed, even the small quantity of light,--which was agreeable before, and which seemed, therefore, to admit of being very safely classed among the sources of pleasure,--is now converted into a source of agony. Since it is impossible, therefore, to fix the limits of pain and pleasure, and every affection or state of mind, agreeable, disagreeable, or indifferent, may, by a very trifling change of circumstance, be converted into an opposite state, it is evident, that any division, founded on this vague and transient distinction, must perplex, and mislead us, in our attempts to systematize the almost infinite diversities of thought and feeling, rather than give us any aid in the arrangement.