E3P55D
Demonstration — Part III
Latin
Mentis essentia id tantum quod mens est et potest, affirmat sive de natura mentis est ea tantummodo imaginari quæ ipsius agendi potentiam ponunt (per propositionem præcedentem). Cum itaque dicimus quod mens dum se ipsam contemplatur, suam imaginatur impotentiam, nihil aliud dicimus quam quod dum mens aliquid imaginari conatur quod ipsius agendi potentiam ponit, hic ejus conatus coercetur sive (per scholium propositionis 11 hujus) quod ipsa contristatur. Q.E.D.
English (Elwes 1883)
The essence of the mind only affirms that which the mind is, or can do; in other words, it is the mind's nature to conceive only such things as assert its power of activity (last Prop.). Thus, when we say that the mind contemplates its own weakness, we are merely saying that while the mind is attempting to conceive something which asserts its power of activity, it is checked in its endeavour----in other words (III. xi. note), it feels pain. Q.E.D.
Modern English
The essence of the mind affirms only what the mind is and can do. Put differently, it is the nature of the mind to imagine only those things that posit its power of acting (E3P54). When we say, then, that the mind in contemplating itself imagines its own powerlessness, we are saying nothing other than that, while the mind strives to imagine something that posits its power of acting, that striving is checked, in other words, (E3P11S), the mind is saddened. Q.E.D.