Proof.- From the true knowledge of good and evil, in so far as it is an emotion, necessarily arises desire (Def. of the Emotions, i.), the strength of which is proportioned to the strength of the emotion wherefrom it arises (III:xxxvii.). But, inasmuch as this desire arises (by hypothesis) from the fact of our truly understanding anything, it follows that it is also present with us, in so far as we are active (III:i.), and must therefore be understood through our essence only (III:Def.ii.); consequently (III:vii.) its force and increase can be defined solely by human power. Again, the desires arising from the emotions whereby we are assailed are stronger, in proportion as the said emotions are more vehement; wherefore their force and increase must be defined solely by the power of external causes, which, when compared with our own power, indefinitely surpass it (IV:iii.); hence the desires arising from like emotions may be more vehement, than the desire which arises from a true knowledge of good and evil, and may, consequently, control or quench it. Q.E.D. Prop. XVI. Desire arising from the knowledge of good and evil, in so far as such knowledge regards what is future, may be more easily controlled or quenched, than the desire for what is agreeable at the present moment. Proof.- Emotion towards a thing, which we conceive as future, is fainter than emotion towards a thing that is present (IV:ix.Coroll.). But desire, which arises from the true knowledge of good and evil, though it be concerned with things which are good at the moment, can be quenched or controlled by any headstrong desire (by the last Prop., the proof whereof is of universal application). Wherefore desire arising from such knowledge, when concerned with the future, can be more easily controlled or quenched, &c. Q.E.D. Prop. XVII. Desire arising from the true knowledge of good and evil, in so far as such knowledge is concerned with what is contingent, can be controlled far more easily still, than desire for things that are present. Proof.- This Prop. is proved in the same way as the last Prop. from IV:xii.Coroll. Note.- I think I have now shown the reason, why men are moved by opinion more readily than by true reason, why it is that the true knowledge of good and evil stirs up conflicts in the soul, and often yields to every kind of passion. This state of things gave rise to the exclamation of the poet: (Ov. Met. vii.20, "Video meliora proboque, Deteriora sequor.") The better path I gaze at and approve,