Book 6

Section 2

Now there are three elements in the soul which control action and the attainment of truth: namely, Sensation, Intellect, and Desire.

Of these, Sensation never originates action, as is shown by the fact that animals have sensation but are not capable of action.

Pursuit and avoidance in the sphere of Desire correspond to affirmation and denial in the sphere of the Intellect. Hence inasmuch as moral virtue is a disposition of the mind in regard to choice, and choice is deliberate desire, it follows that, if the choice is to be good, both the principle must be true and the desire right, and that desire must pursue the same things as principle affirms.

We are here speaking of practical thinking, and of the attainment of truth in regard to action; with speculative thought, which is not concerned with action or production, right and wrong functioning consist in the attainment of truth and falsehood respectively. The attainment of truth is indeed the function of every part of the intellect, but that of the practical intelligence is the attainment of truth corresponding to right desire.

Now the cause of action (the efficient, not the final cause) is choice, and the cause of choice is desire and reasoning directed to some end. Hence choice necessarily involves both intellect or thought and a certain disposition of character [ for doing well and the reverse in the sphere of action necessarily involve thought and character].

Thought by itself however moves nothing, but only thought directed to an end, and dealing with action. This indeed is the moving cause of productive activity also, since he who makes some thing always has some further end in view: the act of making is not an end in itself, it is only a means, and belongs to something else. Whereas a thing done is an end in itself: since doing well (welfare ) is the End, and it is at this that desire aims.

Hence Choice may be called either thought related to desire or desire related to thought; and man, as an originator of action, is a union of desire and intellect.

(Choice is not concerned with what has happened already: for example, no one chooses to have sacked Troy; for neither does one deliberate about what has happened in the past, but about what still lies in the future and may happen or not; what has happened cannot be made not to have happened. Hence Agathon is right in saying

This only is denied even to God, The power to make what has been done undone.)
The attainment of truth is then the function of both the intellectual parts of the soul. Therefore their respective virtues are those dispositions which will best qualify them to attain truth.