E3P13D
Demonstration — Part III
Latin
Quamdiu mens quicquam tale imaginatur tamdiu mentis et corporis potentia minuitur vel coercetur (ut in præcedenti propositione demonstravimus) et nihilominus id tamdiu imaginabitur donec mens aliud imaginetur quod hujus præsentem existentiam secludat (per propositionem 17 partis II) hoc est (ut modo ostendimus) mentis et corporis potentia tamdiu minuitur vel coercetur donec mens aliud imaginetur quod hujus existentiam secludit quodque adeo mens (per propositionem 9 hujus) quantum potest imaginari vel recordari conabitur. Q.E.D.
English (Elwes 1883)
So long as the mind conceives anything of the kind alluded to, the power of the mind and body is diminished or constrained (cf. III. xii. Proof); nevertheless it will continue to conceive it, until the mind conceives something else, which excludes the present existence thereof (II. xvii.); that is (as I have just shown), the power of the mind and of the body is diminished, or constrained, until the mind conceives something else, which excludes the existence of the former thing conceived: therefore the mind (III. ix.), as far as it can, will endeavour to conceive or remember the latter. Q.E.D.
Modern English
So long as the mind imagines anything of the kind in question, the power of mind and body is diminished or constrained (E3P12), and the mind will continue to imagine it until it imagines something else whose present existence excludes it (E2P17), that is, as I have just shown, the power of mind and body is diminished or constrained until the mind imagines something that excludes the existence of the first thing. The mind will therefore strive as much as it can (E3P9) to imagine or recall that other thing. Q.E.D.