E4P30D
Demonstration — Part IV
Latin
Id malum vocamus quod causa est tristitiæ (per propositionem 8 hujus) hoc est (per ejus definitionem, quam vide in scholio propositionis 11 partis III) quod nostram agendi potentiam minuit vel coercet. Si igitur res aliqua per id quod nobiscum habet commune, nobis esset mala, posset ergo res id ipsum quod nobiscum commune habet, minuere vel coercere, quod (per propositionem 4 partis III) est absurdum. Nulla igitur res per id quod nobiscum commune habet, potest nobis esse mala sed contra quatenus mala est hoc est (ut jam jam ostendimus) quatenus nostram agendi potentiam minuere vel coercere potest eatenus (per propositionem 5 partis III) nobis est contraria. Q.E.D.
English (Elwes 1883)
We call a thing bad when it is the cause of pain (IV. viii.), that is (by the Def., which see in III. xi. note), when it diminishes or checks our power of action. Therefore, if anything were bad for us through that quality which it has in common with our nature, it would be able itself to diminish or check that which it has in common with our nature, which (III. iv.) is absurd. Wherefore nothing can be bad for us through that quality which it has in common with us, but, on the other hand, in so far as it is bad for us, that is (as we have just shown), in so far as it can diminish or check our power of action, it is contrary to our nature. Q.E.D.
Modern English
We call something bad when it is the cause of sadness (E4P8), that is (by the definition in the scholium of E3P11 (E3P11S)), when it diminishes or checks our power of acting (E3P11S). If, then, some thing were bad for us through what it has in common with us, that thing could through that very common feature diminish or check our power of acting, which (E3P4) is absurd. Nothing, therefore, can be bad for us through what it has in common with us. On the contrary, in so far as a thing is bad for us, that is, in so far as it can diminish or check our power of acting (E3P11S), it is to that extent contrary to us (E3P5).