E4P19D
Demonstration — Part IV
Latin
Boni et mali cognitio est (per propositionem 8 hujus) ipse lætitiæ vel tristitiæ affectus quatenus ejusdem sumus conscii ac proinde (per propositionem 28 partis III) id unusquisque necessario appetit quod bonum et contra id aversatur quod malum esse judicat. Sed hic appetitus nihil aliud est quam ipsa hominis essentia seu natura (per definitionem appetitus, quam vide in scholio propositionis 9 partis III et 1 affectuum definitionem). Ergo unusquisque ex solis suæ naturæ legibus id necessario appetit vel aversatur etc. Q.E.D.
English (Elwes 1883)
The knowledge of good and evil is (IV. viii.) the emotion of pleasure or pain, in so far as we are conscious thereof; therefore, every man necessarily desires what he thinks good, and shrinks from what he thinks bad. Now this appetite is nothing else but man's nature or essence (Cf. the Definition of Appetite, III. ix. note, and Def. of the Emotions, i.). Therefore, every man, solely by the laws of his nature, desires the one, and shrinks from the other, &c. Q.E.D.
Modern English
Knowledge of good and bad is (E4P8) the affect of joy or sadness itself insofar as we are conscious of it. Therefore (E3P28) everyone necessarily desires what he judges good and shuns what he judges bad. But this appetite is nothing other than the very essence or nature of the human being (E3P9S). Therefore everyone necessarily desires or shuns by the laws of his nature alone, etc. Q.E.D.