or essence of the one differs from the nature
or essence of the other. Again, pleasure and pain are passive
states or passions, whereby every man's power or endeavour to
persist in his being is increased or diminished, helped or
hindered (III. xi. and note). But by the endeavour to persist in
its being, in so far as it is attributable to mind and body in
conjunction, we mean appetite and desire (III. ix. note);
therefore pleasure and pain are identical with desire or
appetite, in so far as by external causes they are increased or
diminished, helped or hindered, in other words, they are every
man's nature; wherefore the pleasure and pain felt by one man
differ from the pleasure and pain felt by another man, only in so
far as the nature or essence of the one man differs from the
essence of the other; consequently, any emotion of one
individual only differs, &c. Q.E.D.

Note.--Hence it follows, that the emotions of the animals
which are called irrational (for after learning the origin of
mind we cannot doubt that brutes feel) only differ from man's
emotions, to the extent that brute nature differs from human
nature. Horse and man are alike carried away by the desire of
procreation; but the desire of the former is equine, the desire
of the latter is human. So also the lusts and appetites of
insects, fishes, and birds must needs vary according to the
several natures. Thus, although each individual lives content
and rejoices in that nature belonging to him wherein he has his
being, yet the life, wherein each is content and rejoices, is
nothing else but the idea, or soul, of the said individual, and
hence the joy of one only differs in nature from the joy of
another, to the extent that the essence of one differs from the
essence of another. Lastly, it follows from the foregoing
proposition, that there is no small difference between the joy
which actuates, say, a drunkard, and the joy possessed by a
philosopher, as I just mention here by the way. Thus far I have
treated of the emotions attributable to man, in so far as he is
passive. It remains to add a few words on those attributable to
him in so far as he is active.

PROP. LVIII. Besides pleasure and desire, which are passivities
or passions, there are other emotions derived from pleasure and
desire, which are attributable to us in so far as we are active.

Proof.--When the mind conceives itself and its power of
activity, it feels pleasure (III. liii.): now t