Page "Numerical sight-singing" Paragraph 113

There is a continual debate about the merits of this system as compared to solfege: it holds the advantage that when dealing with abstract concepts such as interval distance a student may easily recognize that the distance between 1 to 5 is larger than the distance between 1 to 4 because of the numerical values assigned ( as compared to Solfege, where comparing Do to Sol and Do to Fa remain completely abstract until sung or played ).

A drawback often pointed out is that numerical numbers are not always " singable ," for example, scale degree 7 ( ti, in solfege ) contains vowels that are hard to tune.