Thomas Tomkins included this wonderful work on his first list of Lessons of worthe and it is from his reference that the words ‘I must’ in the title are taken. There is apparently no connection with the famous Shakespeare song ‘O mistress mine, where are you roaming’ sung by Feste in Twelfth Night (Act II, sc. 3), a text that can be fitted only with difficulty to the tune. However, Vincent Duckles noticed that the ‘Gamble’ Manuscript contains an early seventeenth-century setting of the melody used by Byrd with a different text, by Thomas Campion (see the first and fifth stanzas, above). Although the first line does not correspond to Tomkins’s title, the fifth stanza seems to refer directly to the well-known title.
Byrd’s setting of this song melody is akin in structure and texture to the variations on Go from my window (BK79), and no doubt dates from the same late period of his life. As there, the tune is not always actually present, but the ear supplies it with no problem. It is one his few pieces that seems to take for granted a Flemish-style short-octave keyboard. The work sounds (and feels under the fingers) like a gradually unfolding series of unhurried improvisations, fluid commentaries around the fragmentary phrases of the original melody rather than a systematic application of different techniques to different variations. The curiously timeless quality of the work derives in part from the odd feature that the melody has fourteen bars, rather than the more usual twelve or sixteen. Moreover, within these fourteen bars, several little phrases are repeated and already varied by Byrd, even before reaching the next variation, so that the ear can easily loose the sense of where one variation ends and another begins. No other work by Byrd combines in this particular manner a quiet, meditative atmosphere and an apparently unschematic, free structural approach, along with an immense variety of musical means and melodic ‘matter’.
from notes by Davitt Moroney © 1999