Aristotle, Nicomachean Ethics
H. Rackham, Ed.

we know from this what bad condition is as well, but we also know what good condition is from bodies in good condition, and know what bodies are in good condition from knowing what good condition is. Thus, supposing good condition is firmness of flesh, bad condition must be flabbiness of flesh, and a diet productive of good condition¹ must be a diet producing firmness of flesh.1. [6]

Also, if one of two correlative groups of words is used in several senses, it follows as a rule that the other is used in several senses too: for example, if ‘just’ has more than one meaning, so also has ‘unjust’ and ‘Injustice.’ 1. [7] Now it appears that the terms Justice and Injustice are used in several senses, but as the equivocal uses are closely connected, the equivocation is not detected; whereas in the case of widely different things called by a common name, the equivocation is comparatively obvious: for example （the difference being considerable when it is one of external form）, the equivocal use of the word kleis （key） to denote both the bone² at the base of the neck and the instrument with which we lock our doors.1. [8]

Let us then ascertain in how many senses a man is said to be ‘unjust.’ Now the term ‘unjust’ is held to apply both to the man who breaks the law and the man who takes more than his due, the unfair³ man. Hence it is clear that the law-abiding man and the fair man will both be just. ‘The just’ therefore means that which is lawful and that which is equal or fair, and ‘the unjust’ means that which is illegal and that which is unequal or unfair.