4p31c.md (734B)
1 Hence it follows, that, in proportion as a thing 2 is in harmony with our nature, so is it more useful or better for 3 us, and vice versâ, in proportion as a thing is more useful for 4 us, so is it more in harmony with our nature. For, in so far as 5 it is not in harmony with our nature, it will necessarily be 6 different therefrom or contrary thereto. If different, it can 7 neither be good nor bad (IV. xxix.); if contrary, it will be 8 contrary to that which is in harmony with our nature, that is, 9 contrary to what is good–in short, bad. Nothing, therefore, can 10 be good, except in so far as it is in harmony with our nature; 11 and hence a thing is useful, in proportion as it is in harmony 12 with our nature, and vice versâ. Q.E.D. 13 14