Chapter 57

Every opposite is opposite either as a thing or as an assertion. If it is opposite as an assertion to an assertion, then it makes for affirmation and negation. Now, affirmation is the stating of what belongs to something, as, for example, ‘he is noble. Negation, on the other hand, is the stating of what does not belong to something, as, for example, ‘he is not noble. Both of these are called statements. If, however, the opposites are opposed as things, then either they are stated as of convertibles and constitute relatives which mutually induce and cancel each other, or they are not stated as of convertibles and do not have any relation. These last either change into each other, both being equally natural, and constitute such contraries as heat and cold; or the one changes into the other, whereas the other does not change. The former is natural, but the latter is unnatural and constitutes opposites by privation and habit, such as are sight and blindness. For sight is a habit, as from having, but blindness is a privation of the habit—the sight, that is.

Some contraries have no intermediate, whereas others have. Those which have no intermediate are those of which one or the other, that is to say, one of them, must necessarily be in their subject, or, in other words, in those things of which they are predicated. An example would be sickness and health in the subject body of an animal, for it is absolutely necessary for that body to have either sickness or health.

By sickness we mean every disorder of the nature. Now, those which have an intermediate are those of which one or the other must not necessarily be in the subject, or in the things of which they are predicated. An example is that of white and black, for these are contraries, yet it is not at all necessary for one of them to be in the body, because it is not necessary for every body to be either white or black—there are gray bodies and tawny ones. There is indeed an exception to this in the case of opposites belonging by definition to some nature, as heat does to fire and cold to snow. Now, in the case of those contraries which have intermediates, some of the intermediates have names, as the mean between white and black is called gray. Others, however, have no names, as the mean between just and unjust has no name. In such a case the mean