The do-re-mi scale takes its names from the opening syllables of a medieval hymn
In eleventh-century Italy, Guido of Arezzo noticed that each line of a Latin hymn to St John the Baptist started one step higher than the last. He named six notes after those first syllables, ut, re, mi, fa, sol and la, and singers still use his trick to learn melodies by ear.
The hymn, Ut queant laxis, had words credited to Paulus Diaconus in the 8th century, so every note name was simply the syllable sung at that pitch. Italians swapped the closed ut for the open do in the 1600s, and a seventh syllable, si, was added later to complete the diatonic scale. In the nineteenth century Sarah Glover turned si into ti for English speakers so that each syllable would start with a different letter, which is why Maria sings ti in the Do-Re-Mi number from The Sound of Music. The word solfège itself is just two syllables, sol and fa, stuck together.
Elizabethan England managed with only four syllables, mi, fa, sol and la, repeating three of them to span the octave. Shakespeare turned that scale into a joke: in the 1623 First Folio of King Lear, the scheming Edmund mutters fa, so, la, mi right after speaking of eclipses and divisions, probably tracing three whole tones in a row, a notoriously ominous interval.
Two rival systems coexist today. In movable do the syllables mark positions in the scale, so do is always the first note of whatever major key a tune happens to be in, and a change of key means reassigning them. It dominates in Britain, the United States, Australia, China and Japan, and it underpins Hungary's Kodály method, along with the hand signs devised by the English educator John Curwen, which climb as the pitch climbs. In fixed do each syllable is welded to one pitch, with do always meaning C.
Fixed do took hold because Italian voice teachers used Guido's syllables for vocal technique, and the Paris Conservatoire copied their conventions in its textbooks when it opened at the turn of the nineteenth century. In Romance and Slavic languages the syllables serve as the ordinary note names, so a French or Italian musician says Beethoven's Ninth Symphony is in re minor. In the latter half of the 19th century the seven syllables even became the vocabulary of an invented language, Solresol.
Source: Solfège
