The chief element of the project consists in the substitution of a relative series of notes or symbols in place of an absolute series. In the common notation any given note, say the A of the treble clef, is uniformly represented by the same symbol, namely, the position of second space in the clef, whatever key it may belong to. Rousseau, insisting on the varying quality impressed on any tone of a given pitch by the key-note of the scale to which it belongs, protested against the same name being given to the tone, however the quality of it might vary. Thus Re or D, which is the second tone in the key of C, ought, according to him, to have a different name when found as the fifth in the key of G, and in every case the name should at once indicate the interval of a tone from its key-note. His mode of effecting this change is as follows. The names ut, re, and the rest, are kept for the fixed order of the tones, C, D, E, and the rest. The key of a piece is shown by prefixing one of these symbols, and this determines the absolute quality of the melody as to pitch. That settled, every tone is expressed by a number bearing a relation to the key-note. This tonic note is represented by one, the other six tones of the scale are expressed by the numbers from two to seven. In the popular Tonic Sol-Fa notation, which corresponds so closely to Rousseau’s in principle, the key-note is always styled Do, and the other symbols, mi, la, and the rest, indicate at once the relative position of these tones in their particular key or scale. Here the old names were preserved as being easily sung; Rousseau selected numbers because he supposed that they best expressed the generation of the sounds.[328]