Understanding or lack of understanding in virtue of which we call men “men of understanding” or “men void of understanding”, are neither entirely the same as scientific knowledge or opinion (for in this case all men would have been men of understanding), nor are they one of the particular sciences, such as medicine concerning the objects of health, or geometry concerning magnitudes; for understanding is concerned neither with what is eternal and unchangeable nor with whatever comes to be, but with things about which one may be puzzled and deliberate. For this reason understanding deals with the same things as practical wisdom but are not the same; for practical wisdom dictates what we ought to do or not to do, which is its end, whereas understanding only judges. For understanding is identical with good understanding (the former implies the later), and men of understanding with men of good understanding.
But understanding is neither the possession nor the acquisition of practical wisdom; but as learning is called understanding when we make use of scientific knowledge, so also understanding is producing when we make use of opinion in order to judge what someone else says about matters with which practical wisdom is concerned, and to judge them well — for good and well are the same thing. And is from this that the name “understanding” is derived, in virtue of which we call ourselves “men of good understanding”, viz. from the implication of the name in learning, since we often call “learning” “understanding”.
Bibliography: Aristotle, Nicomachean Ethics (1142b.34 έως 1143a.18)
Translation: George Kotsalis