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.
Aristotle. Aristotle: The Complete Works (p. 26). Pandora's Box. Kindle Edition.
Can you please suggest where is my mistake in understanding:
Thing is either subject or predicate. If A is present in a subject then it is not subject. If it is not subject then it is predicate. But A is never predicable of a subject.
Certain point of grammatical knowledge is present in the mind
Certain point of grammatical knowledge is Subject. Present in the mind is Predicate. Why Aristotle uses 'present in a subject' but not 'predicable of some supreme object'?