אתיקה, חלק IV, משפט 33

The nature or essence of the emotions cannot be explained solely through our essence or nature (III. Deff. i., ii.), but it must be defined by the power, that is (III. vii.), by the nature of external causes in comparison with our own; hence it follows, that there are as many kinds of each emotion as there are external objects whereby we are affected (III. lvi.), and that men may be differently affected by one and the same object (III. li.), and to this extent differ in nature; lastly, that one and the same man may be differently affected towards the same object, and may therefore be variable and inconstant. Q.E.D.