Part 11

That the contrary of a good is an evil is shown by induction: the contrary of health is disease, of courage, cowardice, and so on. But the contrary of an evil is sometimes a good, sometimes an evil. For defect, which is an evil, has excess for its contrary, this also being an evil, and the mean, which is a good, is equally the contrary of the one and of the other. It is only in a few cases, however, that we see instances of this: in most, the contrary of an evil is a good.

Examples show that the opposite of a good is an evil. The opposite of health is disease, and the opposite of courage is cowardice, and so on. But the opposite of an evil is sometimes a good and sometimes an evil. For example, deficiency is an evil, and its opposite, excess, is also an evil. The middle ground is a good and is equally the opposite of both deficiency and excess. However, we see only a few cases where one evil is the opposite of another. In most cases, the opposite of an evil is a good.

In the case of contraries, it is not always necessary that if one exists the other should also exist: for if all become healthy there will be health and no disease, and again, if everything turns white, there will be white, but no black. Again, since the fact that Socrates is ill is the contrary of the fact that Socrates is well, and two contrary conditions cannot both obtain in one and the same individual at the same time, both these contraries could not exist at once: for if that Socrates was well was a fact, then that Socrates was ill could not possibly be one.

With contraries, the existence of one does not always require the existence of the other. For if everyone becomes healthy, there will be health but no disease. Again, if everything turns white, there will be white but no black. Again, the fact that Socrates is ill is contrary to the fact that Socrates is well. Two contrary conditions cannot both hold in the same individual at the same time. So these two contrary facts could not both be true at once. For if Socrates was well, Socrates could not possibly also be ill.

It is plain that contrary attributes must needs be present in subjects which belong to the same species or genus. Disease and health require as their subject the body of an animal; white and black require a body, without further qualification; justice and injustice require as their subject the human soul.

Clearly, opposite attributes must occur in subjects belonging to the same species or genus. Disease and health require an animal’s body as their subject. White and black require a body, with no further qualification. Justice and injustice require the human soul as their subject.

Moreover, it is necessary that pairs of contraries should in all cases either belong to the same genus or belong to contrary genera or be themselves genera. White and black belong to the same genus, colour; justice and injustice, to contrary genera, virtue and vice; while good and evil do not belong to genera, but are themselves actual genera, with terms under them.

Moreover, every pair of opposites must belong to the same genus, belong to opposite genera, or themselves be genera. White and black belong to the same genus, colour. Justice and injustice belong to opposite genera, virtue and vice. But good and evil do not belong to genera. They are themselves genera, with other terms falling under them.