He’s a former senator. (He used to be a senator at some time in the past, but isn’t now) He’s my former English teacher. (He used to be my English teacher. ) Who was your previous English teacher? (Who was your teacher before your current one?) His previous move in the chess game was a blunder. (His last move) They can be used interchangeably in certain constructions: She’s his ex-girlfriend. (She once was his girlfriend) She’s his former girlfriend. (She once was his girlfriend) She’s a previous girlfriend. (She once was his girlfriend) She’s his previous girlfriend. (She was his last girlfriend)