과거의 상태를 나타낸다고 보면 된다.

am/is(present) -> was(past)

I'm tired. -> I was tired.
He's a girl. -> He was a girl.
Tom is a teacher. -> Tom was a teacher.

I'm not a software engineer. -> I was not a software engineer.
She's not a mom. -> She wasn't a mom.
It isn't delicious. -> It wasn't delicious.

Q: Is she lovely? -> Was she lovely?
A: Yes, she is. -> Yes, she was.

Q: Am I a good man? -> Was I a good man?
A: No, you aren't. -> No, you weren't.

Q: Isn't his father handsome? -> Wasn't his father handsome?
A: Yes, he isn't. -> Yes, he wasn't.

are(present) -> were(past)

They're friends. -> They were friends.
You're a nice guy. -> You were a nice guy.
Were artists. -> We were artists.

You and I aren't a couple. -> You and I weren't a couple.
They're not smart. -> They weren't smart.
His parents aren't from singapore. -> His parents weren't from singapore.

Q: Are you thirsty? -> Were you thirsty?
A: No, I'm not. -> No, I weren’t.

Q: Are they baby? -> Were they baby?
A: Yes, they are. -> Yes, they were.

Q: Are her friends at work? -> Were her friends at work?
A: Yes, they are. -> Yes, they were.