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.