 Another key may be treated as a temporary tonic, called tonicization.In common practice period compositions, and most of the Western popular music of the 20th century, pieces always begin and end in the same key, even if (as in some Romantic-era music) the key is deliberately left ambiguous at first.Some arrangements of popular songs, however, modulate sometime during the song (often in a repeat of the final chorus) and thus end in a different key.