3p27d.md (950B)
1 The images of things are modifications of the human 2 body, whereof the ideas represent external bodies as present to 3 us (II. xvii.); in other words (II. x.), whereof the ideas 4 involve the nature of our body, and, at the same time, the nature 5 of the external bodies as present. If, therefore, the nature of 6 the external body be similar to the nature of our body, then the 7 idea which we form of the external body will involve a 8 modification of our own body similar to the modification of the 9 external body. Consequently, if we conceive anyone similar to 10 ourselves as affected by any emotion, this conception will 11 express a modification of our body similar to that emotion. 12 Thus, from the fact of conceiving a thing like ourselves to be 13 affected with any emotion, we are ourselves affected with a like 14 emotion. If, however, we hate the said thing like ourselves, we 15 shall, to that extent, be affected by a contrary, and not 16 similar, emotion. Q.E.D. 17 18