«زيد كاتب»
Zayd is a writer.
Subject: Zayd, a determinate person.
Predicate: writer, a person who writes.
Predicative relation: affirmation of being a writer of Zayd.
Grasping the two concepts separately does not yet affirm anything. When the statement attributes authorship or writing to Zayd, the subject and predicate are brought together in one referent. That is the structure of predication here.