Predicate Adjective (Describes subject.)
- I am ready.
John is happy.
Sue is sad.
The above sentences can be reversed, thus:
- Ready am I.
Happy is John.
Sad is Sue.
While the previous sentences are unlikely, they are possible. The predicate adjective can change places with the subject.
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Predicate Nominative (Defines subject.)
- John is a plumber.
Mike is a vet.
Richard is a teacher.
Cas is a Canadian.
The predicate nominative
cannot change places with the subject.