P4: There is no affection of the Body of which we cannot form a clear and distinct concept.

Dem.: Those things that are common to all can only be conceived adequately (by IIP38), and so (by IIP12 and L2) there is no affection of the Body of which we cannot form some clear and distinct concept, q.e.d.

Cor.: From this it follows that there is no affect of which we cannot form some clear and distinct concept. For an affect is an idea of an affection of the Body (by Gen. Def. Aff.), which therefore (by P4) must involve some clear and distinct concept.

Schol.: There is nothing from which some effect does not follow (by IP36), and we understand clearly and distinctly whatever follows from an idea which is adequate in us (by IIP40); hence, each of us has—in part, at least, if not absolutely—the power to understand himself and his affects, and consequently, the power to bring it about that he is less acted on by them.

We must, therefore, take special care to know each affect clearly and distinctly (as far as this is possible), so that in this way the Mind may be determined from an affect to thinking those things which it perceives clearly and distinctly, and with which it is fully satisfied, and so that the affect itself may be separated from the thought of an external cause and joined to true thoughts. The result will be not only that Love, Hate, etc., are destroyed (by P2), but also that the appetites, or Desires, which usually arise from such an affect, cannot be excessive (by IVP61).

For it must particularly be noted that the appetite by which a man is said to act, and that by which he is said to be acted on, are one and the same. For example, we have shown that human nature is so constituted that each of us wants the others to live according to his temperament (see IIIP31 S). And indeed, in a man who is not led by reason this appetite is the passion called Ambition, which does not differ much from Pride. On the other hand, in a man who lives according to the dictate of reason it is the action, or virtue, called Morality (see IVP37 S1 and P37 Alternate dem.).

In this way, all the appetites, or Desires, are passions only insofar as they arise from inadequate ideas, and are counted as virtues when they are aroused or generated by adequate ideas. For all the Desires by which we are determined to do something can arise as much from adequate ideas as from inadequate ones (by IVP59). And—to return to the point from which I have digressed—we can devise no other remedy for the affects which depends on our power and is more excellent than this, which consists in a true knowledge of them. For the Mind has no other power than that of thinking and forming adequate ideas, as we have shown (by IIIP3) above.