«فهو ما حكم فيها بثبوت شيء لشيء أو نفيه عنه»
It is a proposition in which something is affirmed of a thing or denied of it.
In “Zayd is standing,” standing is affirmed of Zayd. In “Zayd is not standing,” standing is denied of him. In either case, Zayd is directly the subject of the predication.
Thus categorical propositions need not be affirmative. Both affirmation and denial occur within the categorical form.