Where do the singing syllables "do-re-mi" come from?

Every solfège syllable you've ever sung—do, re, mi, fa, sol, la—comes from a single medieval hymn. The Italian monk Guido of Arezzo took the six half-lines of "Ut queant laxis," a hymn whose melody rises by one step with each line, and used their opening syllables, ut-re-mi-fa-sol-la, as a mnemonic for the notes of the scale, a memory aid that went hand in hand with his other teaching innovation, staff notation.

The trick solved a real problem. In the prologue to his antiphonary, Guido complained about how much time singers spent memorizing music, and explained that his system, built on the staff notation he is credited with developing, would remove the need for memorization. With this approach, once at Arezzo, he cut the standard ten-year training period for a cantor down to just one or two years.

The speed of his method drew attention across Italy, but it also provoked jealousy from monks who felt threatened by his innovations, so around 1025 Guido left Pomposa Abbey for Arezzo, where Bishop Tedald put him in charge of training the cathedral's singers. Word of his teaching eventually reached Pope John XIX, who summoned Guido to Rome to explain his methods.

The syllables kept changing after Guido's death: the composer Giovanni Battista Doni later swapped "Ut" for "Do," a seventh syllable, "Si," was added from the initials of "Sancte Iohannes" (Saint John), and in the 19th century Sarah Glover changed "Si" to "Ti" in English-speaking countries so that every syllable began with a different letter.