Propositions 15 to 24

33. When we love a thing similar to ourselves we endeavour, as far as we can, to bring about that it should love us in return.

Proof: That which we love we endeavour, as far as we can, to conceive in preference to anything else (3.12).

If the thing be similar to ourselves, we shall endeavour to affect it pleasurably in preference to anything else (3.29). In other words, we shall endeavour, as far as we can, to bring it about, that the thing should be affected with pleasure accompanied by the idea of ourselves, that is (3.13 note), that it should love us in return. Q.E.D.

34. The greater the emotion with which we conceive a loved object to be affected towards us, the greater will be our complacency.

35. If anyone conceives, that an object of his love joins itself to another with closer bonds of friendship than he himself has attained to, he will be affected with hatred towards the loved object and with envy towards his rival.

36. He who remembers a thing, in which he has once taken delight, desires to possess it under the same circumstances as when he first took delight therein. Proof= Everything, which a man has seen in conjunction with the object of his love, will be to him accidentally a cause of pleasure (3.15). He will, therefore, desire to possess it, in conjunction with that wherein he has taken delight; in other words, he will desire to possess the object of his love under the same circumstances as when he first took delight therein. Q.E.D.

Corollary= A lover will, therefore, feel pain if one of the aforesaid attendant circumstances be missing.

37. Desire arising through pain or pleasure, hatred or love, is greater in proportion as the emotion is greater.