In music, a refrain has two parts: the lyrics of the song, and the melody. Sometimes refrains use slightly different words as they are repeated. Such lines are still able to be recognised as part of the refrain by the fact that it is always has the same tune or melody. The rhymes, if present, are also kept even if the words are sometimes different. In popular music, the chorus contrasts with the verse, which leads into it, while the bridge contrasts with and leads into both. Many popular songs from the middle of the 20th century consist only of a chorus.