When it comes to choosing a system of syllables to sing for teaching ear training and sight singing, there seems to be a consensus that moveable do, sometimes called functional solfege, is needed for teaching chord and tone functions. To be sure, moving do to wherever the tonic is does help a singer remember where the tonic and other functions are. With practice, students can sing the tonic on do from any pitch at any point in a melody, and the function of chordal patterns can easily be identified by the combinations of moveable do syllables present; for example, any combination of do, mi, and so is a tonic patterns, and any combination of ti, re, fa, and/or so is a dominant pattern. The advantages of moveable do are in force as long as the work begin done is aural; but as soon as music reading is introduced, those advantages all but disappear and are replaced with illogic and difficulty.
Trying to learn to read music with moveable do is confusing, because pitches in identical places on the staff can be known by any one of seven names, twelve if chromatic syllables are used. While the advantages of avoiding this kind of situation are valued for rhythm syllables, they seem to be ignored for tonal syllables. Gordon opposes the Kodaly rhythm syllables, because macro beats are sometimes called ta, sometimes ti, and sometimes ter, yet he does not see a problem with having, for example, a C being sometimes called Do, sometimes Mi, sometimes So, and so forth. This difficulty, like the one with rhythm syllables, is avoidable.
Emile Jaques-Dalcroze was a professor of solfege and harmony at the Geneva Conservatory. Today, he is known for his method of teaching music known as eurhythmics, but solfege training using fixed do was an equally important part of his pedagogy. What interests us about his approach is that he used fixed do solfege to teach pitch and chord functions, something that many today don’t realize is even possible.
Dalcroze began with teaching students to hear the difference between a whole step and a half step. He believed that “every good musical method must be based on the “hearing” of sounds as much as on their performance.” From recognizing whole steps and half steps, he then went on to studying his unique form of scales. All scales were sung in fixed do solfege, from do to do (c to c). By adding the needed sharps or flats, Dalcroze would teach his students all of the scales, but always starting on do, singing up to the next do, and then finishing on the tonic. For example, a B-flat scale would be C, D, E-flat, F, G, A, B-flat, C, B-flat. The student would learn what scale was being sung by the placement of whole steps and half steps, and by audiating the tonic. The beginning note would have different functions, depending on the scale. In the case of the B-flat scale, the beginning tone is the supertonic, and the first half step comes after the second tone. If A-flat and D-flat were added, the beginning tone would be the mediant, and the first half step would come after the first tone. To help the student contextualize the tones in the major tonality, the teacher harmonizes the scale on the piano as the students sing until such assistance is no longer needed and the students can audiate the harmonization on their own. Using the piano to teach the harmonization also avoids students from audiating, for example, the B-flat scale as Aeolian. Only major scales are used at first. Once these are securely learned, it is a small matter to audiate the tonic of minor scales in a similar way.
You may wish to try this method out for yourself. Here are the scales written out. Remember to use fixed do for each scale. It is no longer common practice to use chromatic syllables, so us the same syllable for natural, flat or sharp on each pitch class.