Curse you, you predicate nominative; a grammar lesson

The nominative or subjective case = pro-nouns functioning as the subject.

Pro-nouns

I
You
He
She
It
They

Nominative case

I am an alien.
(True. I'm an American living in South Korea.)

You are an alien.
(I have no idea whether this is true for you.)

He may be an alien... or warlock. 

The predicate nominative is a noun our pronoun after a linking verb that renames the subject.

Three linking verbs

is
am
are

Predicate nominative

The doctors are they.
The detective is me.
The happiest students are I and he. 

Passive voice, oh my!

Grammar books say that the predicate nominative sounds too formal for speech, it should be used in formal writing. I would like to add the caveat, that it should be used rarely, because the predicate nominative is passive.

"The doctors are they," is passive.  "They are the doctors," is active.

So, if your critiques say you have a problem with passive voice, there is a good chance you may have caught a case of the predicate nominative.

Homework- make the following sentences active.

The crazy person is she.
The psychopath is he.
The clowns are they.
The idiot is me.