Propositions 15 to 24by Spinoza
25. We endeavour to affirm, concerning ourselves, and concerning what we love, everything that we can conceive to affect pleasurably ourselves, or the loved object.
On the contrary, we endeavour to negative everything, which we conceive to affect painfully ourselves or the loved object.
26. We endeavour to affirm, concerning that which we hate, everything which we conceive to affect it painfully.
Contrariwise, we endeavour to deny, concerning it, everything which we conceive to affect it pleasurably.
- By the very fact that we conceive a thing, which is like ourselves, and which we have not regarded with any emotion, to be affected with any emotion, we are ourselves affected with a like emotion (affectus).
If we conceive that anyone, whom we have hitherto regarded with no emotion, pleasurably affects something similar to ourselves, we shall be affected with love towards him.
If, on the other hand, we conceive that he painfully affects the same, we shall be affected with hatred towards him.
We cannot hate a thing which we pity, because its misery affects us painfully.
We seek to free from misery, as far as we can, a thing which we pity.
Note 2= This will or appetite for doing good, which arises from pity of the thing whereon we would confer a benefit, is called benevolence, and is nothing else but desire arising from compassion. Concerning love or hate towards him who has done good or harm to something, which we conceive to be like ourselves, see 3.22. note.
28. We endeavour to bring about whatsoever we conceive to conduce to pleasure.
But we endeavour to remove or destroy whatsoever we conceive to be truly repugnant thereto, or to conduce to pain.
29. We shall also endeavour to do whatsoever we conceive men to regard with pleasure, and contrariwise we shall shrink from doing that which we conceive men to shrink from.
 By “men” in this and the following propositions, I mean men whom we regard without any particular emotion.
30. If anyone has done something which he conceives as affecting other men pleasurably, he will be affected by pleasure, accompanied by the idea of himself as cause.
In other words, he will regard himself with pleasure. On the other hand, if he has done anything which he conceives as affecting others painfully, he will regard himself with pain.
31. If we conceive that anyone loves, desires, or hates anything which we ourselves love, desire, or hate, we shall thereupon regard the thing in question with more steadfast love, etc.
On the contrary, if we think that anyone shrinks from something that we love, we shall undergo vacillations of soul.
From the foregoing, and also from 3.28 it follows that everyone endeavours, as far as possible, to cause others to love what he himself loves, and to hate what he himself hates= as the poet says= “As lovers let us share every hope and every fear= ironhearted were he who should love what the other leaves."  Ovid, “Amores,” 2.19. 4,5. Spinoza transposes the verses.