E3P25D
Demonstration — Part III
Latin
Quod rem amatam lætitia vel tristitia afficere imaginamur, id nos lætitia vel tristitia afficit (per propositionem 21 hujus). At mens (per propositionem 12 hujus) ea quæ nos lætitia afficiunt, quantum potest conatur imaginari hoc est (per propositionem 17 partis II et ejus corollarium) ut præsentia contemplari et contra (per propositionem 13 hujus) quæ nos tristitia afficiunt, eorum existentiam secludere; ergo id omne de nobis deque re amata affirmare conamur quod nos vel rem amatam lætitia afficere imaginamur et contra. Q.E.D.
English (Elwes 1883)
That, which we conceive to affect an object of our love pleasurably or painfully, affects us also pleasurably or painfully (III. xxi.). But the mind (III. xii.) endeavours, as far as possible, to conceive those things which affect us pleasurably; in other words (II. xvii. and Coroll.), it endeavours to regard them as present. And, contrariwise (III. xiii.), it endeavours to exclude the existence of such things as affect us painfully; therefore, we endeavour to affirm concerning ourselves, and concerning the loved object, whatever we conceive to affect ourselves, or the love object pleasurably. Q.E.D.
Modern English
What we conceive to affect a loved thing with joy or sadness affects us with joy or sadness in turn (E3P21). The mind (E3P12) strives as much as it can to conceive the things that affect us with joy, that is (E2P17), to regard them as present, and contrariwise (E3P13) strives to exclude the existence of things that affect us with sadness. Therefore we strive to affirm of ourselves and of what we love everything we conceive to affect ourselves or the loved thing with joy, and contrariwise. Q.E.D.