A predicate may be a word or an entire clause. A clausal predicate contains a further predication and can provide a more detailed or emphatic organization than a single adjective.
«زيد أبوه قائم»
Zayd—his father is standing.
Within «أبوه قائم», «أبوه» is the inner subject and «قائم» the inner predicate. The whole clause is then predicated of Zayd and connected to him through the pronoun.
The source relates nominal clauses to settled attribution, verbal clauses to occurrence or renewal, and conditional clauses to conditions of realization. These are rhetorical tendencies shaped by context, not mechanical formulas.