E2P23D
Demonstration — Part II
Latin
Mentis idea sive cognitio (per propositionem 20 hujus) in Deo eodem modo sequitur et ad Deum eodem modo refertur ac corporis idea sive cognitio. At quoniam (per propositionem 19 hujus) mens humana ipsum humanum corpus non cognoscit hoc est (per corollarium propositionis 11 hujus) quoniam cognitio corporis humani ad Deum non refertur quatenus humanæ mentis naturam constituit; ergo nec cognitio mentis ad Deum refertur quatenus essentiam mentis humanæ constituit atque adeo (per idem corollarium propositionis 11 hujus) mens humana eatenus se ipsam non cognoscit. Deinde affectionum quibus corpus afficitur ideæ naturam ipsius corporis humani involvunt (per propositionem 16 hujus) hoc est (per propositionem 13 hujus) cum natura mentis conveniunt; quare harum idearum cognitio cognitionem mentis necessario involvet; at (per propositionem præcedentem) harum idearum cognitio in ipsa humana mente est; ergo mens humana eatenus tantum se ipsam novit. Q.E.D.
English (Elwes 1883)
The idea or knowledge of the mind (II. xx.) follows in God in the same manner, and is referred to God in the same manner, as the idea or knowledge of the body. But since (II. xix.) the human mind does not know the human body itself, that is (II. xi. Coroll.), since the knowledge of the human body is not referred to God, in so far as he constitutes the nature of the human mind; therefore, neither is the knowledge of the mind referred to God, in so far as he constitutes the essence of the human mind; therefore (by the same Coroll. II. xi.), the human mind thus far has no knowledge of itself. Further the ideas of the modifications, whereby the body is affected, involve the nature of the human body itself (II. xvi.), that is (II. xiii.), they agree with the nature of the mind; wherefore the knowledge of these ideas necessarily involves knowledge of the mind; but (by the last Prop.) the knowledge of these ideas is in the human mind itself; wherefore the human mind thus far only has knowledge of itself. Q.E.D.
Modern English
The idea or knowledge of the mind (E2P20) follows in God and is referred to God in the same manner as the idea or knowledge of the body. But since (E2P19) the human mind does not know the human body itself, that is (E2P11C), since the knowledge of the human body is not referred to God insofar as he constitutes the nature of the human mind, neither is the knowledge of the mind referred to God insofar as he constitutes the essence of the human mind. Therefore by that same corollary (E2P11C), the human mind so far does not know itself.
The ideas of the affections by which the body is affected involve the nature of the human body itself (E2P16), that is, (E2P13), they agree with the nature of the mind. Knowledge of these ideas therefore necessarily involves knowledge of the mind. But (E2P22) knowledge of these ideas is in the human mind itself. Therefore the human mind knows itself only to that extent. Q.E.D.