virtue, or would desire it only for the other benefits which it might
produce to himself or to persons whom he cared for.

We have now, then, an answer to the question, of what sort of proof the
principle of utility is susceptible. If the opinion which I have now
stated is psychologically true--if human nature is so constituted as to
desire nothing which is not either a part of happiness or a means of
happiness, we can have no other proof, and we require no other, that
these are the only things desirable. If so, happiness is the sole end of
human action, and the promotion of it the test by which to judge of all
human conduct; from whence it necessarily follows that it must be the
criterion of morality, since a part is included in the whole.

And now to decide whether this is really so; whether mankind do desire
nothing for itself but that which is a pleasure to them, or of which the
absence is a pain; we have evidently arrived at a question of fact and
experience, dependent, like all similar questions, upon evidence. It can
only be determined by practised self-consciousness and self-observation,
assisted by observation of others. I believe that these sources of
evidence, impartially consulted, will declare that desiring a thing and
finding it pleasant, aversion to it and thinking of it as painful, are
phenomena entirely inseparable, or rather two parts of the same
phenomenon; in strictness of language, two different modes of naming the
same psychological fact: that to think of an object as desirable (unless
for the sake of its consequences), and to think of it as pleasant, are
one and the same thing; and that to desire anything, except in
proportion as the idea of it is pleasant, is a physical and metaphysical
impossibility.

So obvious does this appear to me, that I expect it will hardly be