When you hear someone singing a scale (not in nonsense syllables, like “la la la”), you rarely hear them singing the letter names (“C, D, E, F, G”) or the scale degree numbers (“1, 2, 3, 4, 5”). Much more often, singers prefer a system known as solfège, whereby each pitch of the scale is given a different syllable.
The idea behind the system is to create a psychological muscle memory for developing perfect and relative pitch. (Perfect pitch is the ability to recognize and produce pitches accurately in relation to their letter names. Relative pitch is the ability to recognize and produce pitches in relation to each other.) Just as a basketball player needs practice to develop muscle memory to make consistently accurate throws into the basket, musicians need to develop a similar muscle memory so they can accurately find pitches. The solfège system, in creating a different syllable for each pitch, is a tool to help in developing that muscle memory.
The solfège system comes in two-flavors, called “fixed-Do” and “movable-Do.” Fixed-Do solfège is built around the C major and minor scales and is used to build perfect pitch; a C will always be sung as “Do,” and an A will always be sung as “La.” Movable-Do solfège, on the other hand, is useful for working on relative pitch because it can be shifted to any scale or key. In the movable-Do system, the root of the scale is always your Do.
My personal preference is for movable-Do solfège because for almost all musical applications outside transcription, you don’t need perfect pitch. Being able to identify and reproduce pitch intervals, melodically and harmonically, is a much more valuable tool as a performer and as a composer. The remainder of the solfège discussion here will use movable-Do solfège.
The major scale is named, in ascending order, “Do, Re, Mi, Fa, So, La, Ti” before returning to Do. The natural minor scale is named, in ascending order, “Do, Re, Me, Fa, So, Le, Te,” and another Do.
You may occasionally encounter “Si” and “Ut” as solfège syllables. Ut was the original Do and was changed to allow an open vowel at the end. Si was the original Ti and was changed so that each syllable starts with a different consonant, heightening the effectiveness of the differentiation between syllables in forming a musical muscle memory.
As described in the article on note names, it is sometimes necessary to give a note a ridiculous name (B double-sharp) for analytical reasons. From a theoretician’s standpoint, it makes complete structural sense, but it can leave you with questions when you have to sing something like that if you don’t understand all that music theory. (Don’t worry; it can get really complicated, and I’ll skip that discussion here.) Solfège does account for altered scale steps by changing the vowel sound.
Note from the minor scale that dropping a note by a half step makes it end in “e.” A comparison of the C major and C minor scales shows these differences. Note the Es (Mi vs. Me), As (La vs. Le), and Bs (Ti vs. Te). If a pitch already ends in “e,” it becomes “a.” (e.g., Re becomes Ra.)
On the other hand, raising a pitch by a half step makes “a” and “e” pitches end in “i” and makes “o” pitches end in “u.” For example, a raised Do becomes Du, and a raised La becomes Li. The only exception is Ti, which becomes To when raised. (Note the similarity between the sounds “To” and “Do,” which are sung as the same pitch. That was no accident.)