grammatical learning and all those qualities which are classed as
dispositions. However that may be, it is an incontrovertible fact
that the things which in virtue of these qualities are said to be
what they are vary in the degree in which they possess them; for
one man is said to be better versed in grammar, or more healthy
or just, than another, and so on.

The qualities expressed by the terms 'triangular' and
'quadrangular' do not appear to admit of variation of degree, nor
indeed do any that have to do with figure. For those things to
which the definition of the triangle or circle is applicable are
all equally triangular or circular. Those, on the other hand, to
which the same definition is not applicable, cannot be said to
differ from one another in degree; the square is no more a circle
than the rectangle, for to neither is the definition of the
circle appropriate. 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