Prop. V. The power and increase of every passion, and its persistence in existing are not defined by the power, whereby we ourselves endeavour to persist in existing, but by the power of an external cause compared with our own.
Proof.- The essence of a passion cannot be explained through our essence alone (III:Def.i.&.ii.), that is (III:vii.), the power of a passion cannot be defined by the power, whereby we ourselves endeavour to persist in existing, but (as is shown in II:xvi.) must necessarily be defined by the power of an external cause compared with our own. Q.E.D.
Prop. VI. The force of any passion or emotion can 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:Def.i.&.ii.), that is (III:vii.), when it increases or diminishes, helps or hinders, our power of activity.
Thus, in so far as we perceive that a thing affects us with pleasure or pain, we call it good or evil; wherefore the knowledge of good and evil is nothing else but the idea of the pleasure or pain, which necessarily follows from that pleasurable or painful emotion (II:xxii.). But this idea is united to the emotion in the same way as mind is united to body (II:xxi.); that is, there is no real distinction between this idea and the emotion or idea of the modification of the body, save in conception only. Therefore the knowledge of good and evil is nothing else but the emotion, in so far as we are conscious thereof. Q.E.D.
Prop. IX. An emotion, whereof we conceive the cause to be with us at the present time, is stronger than if we did not conceive the cause to be with us.
Proof.- Imagination or conception is the idea, by which the mind regards a thing as present (II:xvii.note), but which indicates the disposition of the mind rather than the nature of the external thing (II:xvi.Coroll.ii).
An emotion is therefore a conception, in so far as it indicates the disposition of the body. But a conception (by II:xvii.) is stronger, so long as we conceive nothing which excludes the present existence of the external object; wherefore an emotion is also stronger or more intense, when we conceive the cause to be with us at the present time, than when we do not conceive the cause to be with us. Q.E.D.
Note.- When I said above in III:xviii. that we are affected by the image of what is past or future with the same emotion as if the thing conceived were present, I expressly stated, that this is only true in so far as we look solely to the image of the thing in question itself; for the thing's nature is unchanged, whether we have conceived it or not; I did not deny that the image becomes weaker, when we regard as present to us other things which exclude the present existence of the future object: I did not expressly call attention to the fact, because I purposed to treat of the strength of the emotions in this part of my work.
Corollary.- The image of something past or future, that is, of a thing which we regard as in relation to time past or time future, to the exclusion of time present, is, when other conditions are equal, weaker than the image of something present; consequently an emotion felt towards what is past or future is less intense, other conditions being equal, than an emotion felt towards something present.
Prop. X. Towards something future, which we conceive as close at hand, we are affected more intensely, than if we conceive that its time for existence is separated from the present by a longer interval; so too by the remembrance of what we conceive to have not long passed away we are affected more intensely, than if we conceive that it has long passed away.
