C, is the third of the tonic, and is answered by the third of the dominant; the second E is not followed by a note of the tonic chord, and is therefore regarded as sixth of the dominant. Our next example,
J. S. Bach. Cantata, "Singet dem Herrn ein neues Lied."
illustrates a different point. The first F in the third bar cannot be regarded as belonging to the dominant key, because of the G natural that follows, neither can the second which resolves the preceding G; but the F preceding the G sharp is treated as the submediant of A.
131. The same principles will guide us in dealing with the leading note. Let the fundamental principle be thoroughly grasped that the tonal change must be made as soon as possible, and the whole thing is easy. If a subject modulates, the leading note must be always treated as the third of the dominant, and answered by third of tonic, except when it is merely an auxiliary note of the tonic to which it at once returns, e.g.—
J. S. Bach. Wohltemperirtes Clavier, Fugue 2.
This subject does not modulate, but it shows the use of the leading note as an auxiliary note.
132. The following examples
J. S. Bach. Organ Fugue in C.
J. S. Bach. Wohltemperirtes Clavier, Fugue 18.
