[MikeNewYork]

Originally Posted by RonBee

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.

How about:

John is the plumber.
The plumber is John.

etc.