an overcome the
rest of a man's activities or power, so that the emotion becomes
obstinately fixed to him.

Proof.--The force and increase of any passion and its
persistence in existing are defined by the power of an external
cause compared with our own (by the foregoing Prop.); therefore
(IV. iii.) it can overcome a man's power, &e. Q.E.D.

PROP. VII. An emotion can only be controlled or destroyed by
another emotion contrary thereto, and with more power for
controlling emotion.

Proof.--Emotion, in so far as it is referred to the mind, is
an idea, whereby the mind affirms of its body a greater or less
force of existence than before (cf. the general Definition of the
Emotions at the end of Part III.). When, therefore, the mind is
assailed by any emotion, the body is at the same time affected
with a modification whereby its power of activity is increased or
diminished. Now this modification of the body (IV. v.) receives
from its cause the force for persistence in its being; which
force can only be checked or destroyed by a bodily cause (II.
vi.), in virtue of the body being affected with a modification
contrary to (III. v.) and stronger than itself (IV. Ax.);
wherefore (II. xii.) the mind is affected by the idea of a
modification contrary to, and stronger than the former
modification, in other words, (by the general definition of the
emotions) the mind will be affected by an emotion contrary to and
stronger than the former emotion, which will exclude or destroy
the existence of the former emotion; thus an emotion cannot be
destroyed nor controlled except by a contrary and stronger
emotion. Q.E.D.

Corollary.--An emotion, in so far as it is referred to the
mind, can only be controlled or destroyed through an idea of a
modification of the body contrary to, and stronger than, that
which we are undergoing. For the emotion which we undergo can
only be checked or destroyed by an emotion contrary to, and
stronger than, itself, in other words, (by the general Definition
of the Emotions) only by an idea of a modification of the body
contrary to, and stronger than, the modification which we
undergo.

PROP. VIII. The knowledge of good and evil is nothing else but
the emotions of pleasure or pain, in so far as we are conscious
thereof.

Proof.--We call a thing good or evil, when it is of service or
the reverse in preserving our being (IV. Deff. i. and ii.), that
is (III. vii.), when it increases or diminishes, hel