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In short, if the definition of the term proposed is not applicable

to both objects, they cannot be compared. Thus it is not all qualities

which admit of variation of degree.

Whereas none of the characteristics I have mentioned are peculiar to

quality, the fact that likeness and unlikeness can be predicated

with reference to quality only, gives to that category its distinctive

feature. One thing is like another only with reference to that in

virtue of which it is such and such; thus this forms the peculiar mark

of quality.

We must not be disturbed because it may be argued that, though

proposing to discuss the category of quality, we have included in it

many relative terms. We did say that habits and dispositions were

relative. In practically all such cases the genus is relative, the

individual not. Thus knowledge, as a genus, is explained by

reference to something else, for we mean a knowledge of something. But

particular branches of knowledge are not thus explained. The knowledge

of grammar is not relative to anything external, nor is the

knowledge of music, but these, if relative at all, are relative only

in virtue of their genera; thus grammar is said be the knowledge of

something, not the grammar of something; similarly music is the

knowledge of something, not the music of something.

Thus individual branches of knowledge are not relative. And it is

because we possess these individual branches of knowledge that we

are said to be such and such. It is these that we actually possess: we

are called experts because we possess knowledge in some particular

branch. Those particular branches, therefore, of knowledge, in

virtue of which we are sometimes said to be such and such, are

themselves qualities, and are not relative. Further, if anything

should happen to fall within both the category of quality and that

of relation, there would be nothing extraordinary in classing it under

both these heads.