k what is useful for himself is the foundation
of impiety, rather than of piety and virtue.

Therefore, after briefly showing that the contrary is the
case, I go on to prove it by the same method, as that whereby I
have hitherto proceeded.

PROP. XIX. Every man, by the laws of his nature, necessarily
desires or shrinks from that which he deems to be good or bad.

Proof.--The knowledge of good and evil is (IV. viii.) the
emotion of pleasure or pain, in so far as we are conscious
thereof; therefore, every man necessarily desires what he thinks
good, and shrinks from what he thinks bad. Now this appetite is
nothing else but man's nature or essence (Cf. the Definition of
Appetite, III. ix. note, and Def. of the Emotions, i.).
Therefore, every man, solely by the laws of his nature, desires
the one, and shrinks from the other, &c. Q.E.D.

PROP. XX. The more every man endeavours, and is able to seek
what is useful to him--in other words, to preserve his own
being--the more is he endowed with virtue; on the contrary, in
proportion as a man neglects to seek what is useful to him, that
is, to preserve his own being, he is wanting in power.

Proof.--Virtue is human power, which is defined solely by
man's essence (IV. Def. viii.), that is, which is defined solely
by the endeavour made by man to persist in his own being.
Wherefore, the more a man endeavours, and is able to preserve his
own being, the more is he endowed with virtue, and, consequently
(III. iv. and vi.), in so far as a man neglects to preserve his
own being, he is wanting in power. Q.E.D.

Note.--No one, therefore, neglects seeking his own good, or
preserving his own being, unless he be overcome by causes
external and foreign to his nature. No one, I say, from the
necessity of his own nature, or otherwise than under compulsion
from external causes, shrinks from food, or kills himself: which
latter may be done in a variety of ways. A man, for instance,
kills himself under the compulsion of another man, who twists
round his right hand, wherewith he happened to have taken up a
sword, and forces him to turn the blade against his own heart;
or, again, he may be compelled, like Seneca, by a tyrant's
command, to open his own veins--that is, to escape a greater evil
by incurring, a lesser; or, lastly, latent external causes may
so disorder his imagination, and so affect his body, that it may
assume a nature contrary to its former one, and whereof the idea
can