What If A Day Or A Month Or A Year? is an Ayre, written by the English poet and composer Thomas Campion (1667 – 1620). Obviously, this song was quite popular in Campion’s time, because we know multiple arrangements of it, for instance in the Jane Pickering’s Lute Book. This arrangement was made by John Dowland.
The melody is well-known in Holland as well. Adriaen Valerius (~1570 – 1620) used it for the song Merck toch hoe Sterck, one of the many Protestant songs from his collection Nederlandtsche Gedenck-Clanck.
Dowland uses a common form of arrangement in his days: one line of thematic material is followed by a variation with divisions and elaboration.