E4P18D
Demonstration — Part IV
Latin
Cupiditas est ipsa hominis essentia (per 1 affectuum definitionem) hoc est (per propositionem 7 partis III) conatus quo homo in suo esse perseverare conatur. Quare cupiditas quæ ex lætitia oritur, ipso lætitiæ affectu (per definitionem lætitiæ, quam vide in scholio propositionis 11 partis III) juvatur vel augetur; quæ autem contra ex tristitia oritur, ipso tristitiæ affectu (per idem scholium) minuitur vel coercetur atque adeo vis cupiditatis quæ ex lætitia oritur, potentia humana simul et potentia causæ externæ, quæ autem ex tristitia sola humana potentia definiri debet ac proinde hac illa fortior est. Q.E.D.
English (Elwes 1883)
Desire is the essence of a man (Def. of the Emotions, i.), that is, the endeavour whereby a man endeavours to persist in his own being. Wherefore desire arising from pleasure is, by the fact of pleasure being felt, increased or helped; on the contrary, desire arising from pain is, by the fact of pain being felt, diminished or hindered; hence the force of desire arising from pleasure must be defined by human power together with the power of an external cause, whereas desire arising from pain must be defined by human power only. Thus the former is the stronger of the two. Q.E.D.
Modern English
Desire is the very essence of a human being (E3DA1), that is, (E3P7), the *conatus* by which a human being strives to persist in his being. The desire that arises from joy is therefore aided and increased by the affect of joy itself (E3P11S), while the desire that arises from sadness is diminished or checked by the affect of sadness (E3P11S). The force of desire arising from joy must therefore be defined by both human power and the power of an external cause, while the force of desire arising from sadness must be defined by human power alone. The former is therefore stronger than the latter. Q.E.D.