P59: To every action to which we are determined from an affect which is a passion, we can be determined by reason, without that affect.

Dem.: Acting from reason is nothing but doing those things which follow from the necessity of our nature, considered in itself alone (by IIIP3 and D2). But Sadness is evil insofar as it decreases or restrains this power of acting (by P41). Therefore, from this affect we cannot be determined to any action which we could not do if we were led by reason.

Furthermore, Joy is bad {only} insofar as it prevents man from being capable of acting (by P41 and P43), and so to that extent also, we cannot be determined to any action which we could not do if we were guided by reason.

Finally, insofar as Joy is good, it agrees with reason (for it consists in this, that a man’s power of acting is increased or aided), and is not a passion except insofar as the man’s power of acting is not increased to the point where he conceives himself and his actions adequately.

So if a man affected with Joy were led to such a great perfection that he conceived himself and his actions adequately, he would be capable—indeed more capable—of the same actions to which he is now determined from affects which are passions.

But all affects are related to Joy, Sadness, or Desire (see the explanation of Def. Aff. IV), and Desire (by Def. Aff. I) is nothing but the striving to act itself. Therefore, to every action to which we are determined from an affect which is a passion, we can be led by reason alone, without the affect, q.e.d.

Alternate dem.: Any action is called evil insofar as it arises from the fact that we have been affected with Hate or with some evil affect (see P45 C1). But no action, considered in itself, is good or evil (as we have shown in the Preface of this Part); instead, one and the same action is now good, now evil. Therefore, to the same action which is now evil, or which arises from some evil affect, we can (by P19) be led by reason, q.e.d.

Schol.: These things are more clearly explained by an example. The act of beating, insofar as it is considered physically, and insofar as we attend only to the fact that the man raises his arm, closes his fist, and moves his whole arm forcefully up and down, is a virtue, which is conceived from the structure of the human Body. Therefore, if a man moved by Anger or Hate is determined to close his fist or move his arm, that (as we have shown in Part II) happens because one and the same action can be joined to any images of things whatever. And so we can be determined to one and the same action both from those images of things which we conceive confusedly and {from those images of things?} we conceive clearly and distinctly.

It is evident, therefore, that every Desire that arises from an affect which is a passion would be of no use if men could be guided by reason. Let us see now why we call a Desire blind which arises from an affect which is a passion.