How was the labeling of the musical notes A-G decided?

Question

After all, the note we call "C" is really a more "important" note, and is labeled with the first label "do" in another labeling scale. What made people want to decide to put the label "A" on "la" instead of "do"? How was this system invented in the first place?

Answer 1

"The founder of what is now considered the standard music stave was Guido d'Arezzo, an Italian Benedictine monk who lived from 995–1050 A.D. His revolutionary method—combining a 4 line stave with the first form of notes known as 'neumes'—was the precursor to the five line stave, which was introduced in the 14th century and is still in use today. Guido D'Arezzo's achievements paved the way for the modern form of written music, music books, and the modern concept of a composer."


"The invention of solfege is ascribed to Guido of Arezzo. He used a series of six syllables to refer to the six degrees of the hexachord. These six syllables were drawn from the hymn to Saint John "Ut queant laxis", because each of the six phrases of that hymn began on each of the six degrees of the hexachord:

Ut queant laxis resonare fibris
Mira gestorum famuli tuorum,
Solve polluti labii reatum,
Sancte Ioannes.

This hymn gave the six syllables: Ut, Re, Mi, Fa, Sol, La. In the course of time, "Ut" was changed to "Do" on the grounds that it was easier to sing, and the syllable "Si" was added to indicate the leading tone of the modern scale. (The name "Si" may perhaps derive from the first letters of "sancte ioannes".)"