the emotion of sorrow which arises from one object is of
a different kind from that which arises from another cause, and the same
thing is to be understood of love, hatred, hope, fear, vacillation of
mind, etc.; so that there are necessarily just as many kinds of joy,
sorrow, love, hatred, etc., as there are kinds of objects by which we
are affected. But desire is the essence itself or nature of a person in
so far as this nature is conceived from its given constitution as
determined towards any action, and therefore as a person is affected by
external causes with this or that kind of joy, sorrow, love, hatred,
etc., that is to say, as his nature is constituted in this or that way,
so must his desire vary and the nature of one desire differ from that of
another, just as the emotions from which each desire arises differ.
There are as many kinds of desires, therefore, as there are kinds of
joy, sorrow, love, etc., and, consequently (as we have just shown), as
there are kinds of objects by which we are affected.

All emotions are related to desire, joy, or sorrow, as the definitions
show which we have given of those emotions. But desire is the very
nature or essence of a person and therefore the desire of one person
differs from the desire of another as much as the nature or essence of
the one differs from that of the other. Again, joy and sorrow are
passions by which the power of a person or his effort to persevere in
his own being is increased or diminished, helped, or limited. But by the
effort to persevere in his own being, in so far as it is related at the
same time to the mind and the body, we understand appetite and desire,
and therefore joy and sorrow are desire or appetite in so far as the
latter is increased, diminished, helped, or limited by external causes;
that is to say they are the nature itself of each person.

The joy or sorrow of one person therefore differs from the joy or sorrow
of another as much as the nature or essence of one person differs from
that of the other, and consequently the emotion of one person differs
from the corresponding emotion of another.

Hence it follows that the emotions of animals which are called
irrational (for after we have learned the origin of the mind we can in
no way doubt that brutes feel) differ from human emotions as much as
the nature of a brute differs from that of a man. Both the man and the
horse, for example, are swayed by the lust to propagate, but the horse
is