P13: When the Mind imagines those things that diminish or restrain the Body’s power of acting, it strives, as far as it can, to recollect things that exclude their existence.

Dem.: So long as the Mind imagines anything of this kind, the power both of Mind and of Body is diminished or restrained (as we have demonstrated in P12); nevertheless, the Mind will continue to imagine this thing until it imagines something else that excludes the thing’s present existence (by IIP17), i.e. (as we have just shown), the power both of Mind and of Body is diminished or restrained until the Mind imagines something else that excludes the existence of this thing; so the Mind (by P9), as far as it can, will strive to imagine or recollect that other thing, q.e.d.

Cor.: From this it follows that the Mind avoids imagining those things that diminish or restrain its or the Body’s power.

Schol.: From this we understand clearly what Love and Hate are. Love is nothing but Joy with the accompanying idea of an external cause, and Hate is nothing but Sadness with the accompanying idea of an external cause. We see, then, that one who loves necessarily strives to have present and preserve the thing he loves; and on the other hand, one who hates strives to remove and destroy the thing he hates. But all of these things will be discussed more fully in what follows.