3p15d.md (830B)
1 Let it be granted that the mind is simultaneously 2 affected by two emotions, of which one neither increases nor 3 diminishes its power of activity, and the other does either 4 increase or diminish the said power (III. Post. i.). From the 5 foregoing proposition it is evident that, whenever the mind is 6 afterwards affected by the former, through its true cause, which 7 (by hypothesis) neither increases nor diminishes its power of 8 action, it will be at the same time affected by the latter, which 9 does increase or diminish its power of activity, that is (III. 10 xi. note) it will be affected with pleasure or pain. Thus the 11 former of the two emotions will, not through itself, but 12 accidentally, be the cause of pleasure or pain. In the same way 13 also it can be easily shown, that a thing may be accidentally the 14 cause of desire. Q.E.D. 15 16