It follows, then, that if the purpose is to be all it should be, both the calculation or reasoning must be true and the desire right, and that the very same things must be assented to by the former and pursued by the latter.

This kind of reasoning, then, and this sort of truth has to do with action.

But speculative reasoning that has to do neither with action nor production is good or bad according as it is true or false simply: for the function of the intellect is always the apprehension of truth; but the function of the practical intellect is the apprehension of truth in agreement with right desire.

Purpose, then, is the cause⁠—not the final but the efficient cause or origin⁠—of action, and the origin of purpose is desire and calculation of means; so that purpose necessarily implies on the one hand the faculty of reason and its exercise, and on the other hand a certain moral character or state of the desires; for right action and the contrary kind of action are alike impossible without both reasoning and moral character.