it has in common with our nature, but it is bad for us in
so far as it is contrary to our nature.

Proof.--We call a thing bad when it is the cause of pain (IV.
viii.), that is (by the Def., which see in III. xi. note), when
it diminishes or checks our power of action. Therefore, if
anything were bad for us through that quality which it has in
common with our nature, it would be able itself to diminish or
check that which it has in common with our nature, which (III.
iv.) is absurd. Wherefore nothing can be bad for us through that
quality which it has in common with us, but, on the other hand,
in so far as it is bad for us, that is (as we have just shown),
in so far as it can diminish or check our power of action, it is
contrary to our nature.
Q.E.D.

PROP. XXXI. In so far as a thing is in harmony with our nature,
it is necessarily good.

Proof.--In so far as a thing is in harmony with our nature, it
cannot be bad for it. It will therefore necessarily be either
good or indifferent. If it be assumed that it be neither good
nor bad, nothing will follow from its nature (IV. Def. i.), which
tends to the preservation of our nature, that is (by the
hypothesis), which tends to the preservation of the thing itself;
but this (III. vi.) is absurd; therefore, in so far as a thing
is in harmony with our nature, it is necessarily good. Q.E.D.

Corollary.--Hence it follows, that, in proportion as a thing
is in harmony with our nature, so is it more useful or better for
us, and vice versa, in proportion as a thing is more useful for
us, so is it more in harmony with our nature. For, in so far as
it is not in harmony with our nature, it will necessarily be
different therefrom or contrary thereto. If different, it can
neither be good nor bad (IV. xxix.); if contrary, it will be
contrary to that which is in harmony with our nature, that is,
contrary to what is good--in short, bad. Nothing, therefore, can
be good, except in so far as it is in harmony with our nature;
and hence a thing is useful, in proportion as it is in harmony
with our nature, and vice versa. Q.E.D.

PROP. XXXII. In so far as men are a prey to passion, they
cannot, in that respect, be said to be naturally in harmony.

Proof.--Things, which are said to be in harmony naturally, are
understood to agree in power (III. vii.), not in want of power or
negation, and consequently not in passion (III. iii. note);
wherefore men, in so far as they are a prey to