Categories, Section 1, Part 2

Forms of speech are either simple or composite. Examples of the latter
are such expressions as 'the man runs', 'the man wins'; of the former
'man', 'ox', 'runs', 'wins'.

Of things themselves some are predicable of a subject, and are never
present in a subject. Thus 'man' is predicable of the individual man,
and is never present in a subject.

By being 'present in a subject' I do not mean present as parts are
present in a whole, but being incapable of existence apart from the
said subject.

Some things, again, are present in a subject, but are never predicable
of a subject. For instance, a certain point of grammatical knowledge
is present in the mind, but is not predicable of any subject; or again,
a certain whiteness may be present in the body (for colour requires
a material basis), yet it is never predicable of anything.

Other things, again, are both predicable of a subject and present
in a subject. Thus while knowledge is present in the human mind, it
is predicable of grammar.

There is, lastly, a class of things which are neither present in a
subject nor predicable of a subject, such as the individual man or
the individual horse. But, to speak more generally, that which is
individual and has the character of a unit is never predicable of
a subject. Yet in some cases there is nothing to prevent such being
present in a subject. Thus a certain point of grammatical knowledge
is present in a subject.