That's John, isn't he?

Grammar notes

Positive Sentence, Negative Tag

After a positive statement, the question tag is usually negative. The helper verb in the tag must match the main sentence. We often use tags to check or confirm information.

• Example: That's John, isn't he?
• Example: She can swim, can't she?

Quick Rule

• positive statement -> negative tag
• match the helper verb and the subject in the tag

The main sentence says it; the tag politely checks it.