E3P28D
Demonstration — Part III
Latin
Quod ad lætitiam conducere imaginamur, quantum possumus imaginari conamur (per propositionem 12 hujus) hoc est (per propositionem 17 partis II) id quantum possumus conabimur ut præsens sive ut actu existens contemplari. Sed mentis conatus seu potentia in cogitando æqualis et simul natura est cum corporis conatu seu potentia in agendo (ut clare sequitur ex corollario propositionis 7 et corollario propositionis 11 partis II) : ergo ut id existat absolute conamur sive (quod per scholium propositionis 9 hujus idem est) appetimus et intendimus; quod erat primum. Deinde si id quod tristitiæ causam esse credimus hoc est (per scholium propositionis 13 hujus) si id quod odio habemus, destrui imaginamur, lætabimur (per propositionem 20 hujus) adeoque idem (per primam hujus partem) conabimur destruere sive (per propositionem 13 hujus) a nobis amovere ne ipsum ut præsens contemplemur, quod erat secundum. Ergo id omne quod ad lætitiam etc. Q.E.D.
English (Elwes 1883)
We endeavour, as far as possible, to conceive that which we imagine to conduce to pleasure (III. xii.); in other words (II. xvii.) we shall endeavour to conceive it as far as possible as present or actually existing. But the endeavour of the mind, or the mind's power of thought, is equal to, and simultaneous with, the endeavour of the body, or the body's power of action. (This is clear from II. vii. Coroll. and II. xi. Coroll.). Therefore we make an absolute endeavour for its existence, in other words (which by III. ix. note, come to the same thing) we desire and strive for it; this was our first point. Again, if we conceive that something, which we believed to be the cause of pain, that is (III. xiii. note), which we hate, is destroyed, we shall rejoice (III. xx.). We shall, therefore (by the first part of this proof), endeavour to destroy the same, or (III. xiii.) to remove it from us, so that we may not regard it as present; this was our second point. Wherefore whatsoever conduces to pleasure, &c. Q.E.D.
Modern English
What we imagine conduces to joy we strive as far as possible to conceive (E3P12), that is, by E2P17 (E2P17), we strive to regard it as present and actually existing. But the mind's striving, its power of thinking, is equal in nature and simultaneous with the body's striving, its power of acting, as follows clearly from E2P7C and E2P11C (E2P7C). We therefore strive absolutely for its existence, which is the same thing as, by E3P9S (E3P9S), desiring and intending it. That was the first point.
Then, if we imagine that something we believe to be the cause of sadness, that is, by E3P13S (E3P13S), something we hate, is destroyed, we will rejoice (E3P20). We will therefore strive by the first part of this proof to destroy it, or by E3P13 (E3P13) to remove it from us so that we need not regard it as present. That was the second point. So we strive to bring about everything that conduces to joy, and so on. Q.E.D.