E4P8D
Demonstration — Part IV
Latin
Id bonum aut malum vocamus quod nostro esse conservando prodest vel obest (per definitiones 1 et 2 hujus) hoc est (per propositionem 7 partis III) quod nostram agendi potentiam auget vel minuit, juvat vel coercet. Quatenus itaque (per definitiones lætitiæ et tristitiæ, quas vide in scholio propositionis 11 partis III) rem aliquam nos lætitia vel tristitia afficere percipimus, eandem bonam aut malam vocamus atque adeo boni et mali cognitio nihil aliud est quam lætitiæ vel tristitiæ idea quæ ex ipso lætitiæ vel tristitiæ affectu necessario sequitur (per propositionem 22 partis II). At hæc idea eodem modo unita est affectui ac mens unita est corpori (per propositionem 21 partis II) hoc est (ut in scholio ejusdem propositionis ostensum) hæc idea ab ipso affectu sive (per generalem affectuum definitionem) ab idea corporis affectionis revera non distinguitur nisi solo conceptu; ergo hæc cognitio boni et mali nihil est aliud quam ipse affectus quatenus ejusdem sumus conscii. Q.E.D.
English (Elwes 1883)
We call a thing good or evil, when it is of service or the reverse in preserving our being (IV. Deff. i. and ii.), that is (III. vii.), when it increases or diminishes, helps or hinders, our power of activity. Thus, in so far as we perceive that a thing affects us with pleasure or pain, we call it good or evil; wherefore the knowledge of good and evil is nothing else but the idea of the pleasure or pain, which necessarily follows from that pleasurable or painful emotion (II. xxii.). But this idea is united to the emotion in the same way as mind is united to body (II. xxi.); that is, there is no real distinction between this idea and the emotion or idea of the modification of the body, save in conception only. Therefore the knowledge of good and evil is nothing else but the emotion, in so far as we are conscious thereof. Q.E.D.
Modern English
We call a thing good or bad according to whether it aids or hinders the preservation of our being (E4D1), that is, (E3P7), according to whether it increases or diminishes our power of acting. Insofar as we perceive (E3P11S) that something affects us with joy or sadness, we therefore call it good or bad. The knowledge of good and bad is accordingly nothing other than the idea of joy or sadness that necessarily follows from the affect of joy or sadness itself (E2P22). But this idea is united to the affect in the same way as mind is united to body (E2P21), that is, as shown in the scholium of that proposition, this idea is not really distinct from the affect itself, or from the idea of the bodily affection, except in conception alone. The knowledge of good and bad is therefore nothing other than the affect itself insofar as we are conscious of it. Q.E.D.