Page:Fugue by Ebenezer Prout.djvu/71

answer to the subject is obtained than if the modulation be regarded as taking place later. Sometimes, however, the form of the subject does not admit of an early change—

J. S. Bach. Toccata and Fugue for Organ, in C.

The first notes of this subject were spoken of in § 93. It is impossible here to regard the modulation as taking place till after the subdominant harmony at (a). The length and variety of this subject render it a very suitable illustration of the rules we gave in § 122. The student will here see nearly every note of the scale of C in both its relations; we have even at (b) the rare case of the subdominant considered as the minor seventh of the dominant.

127. It is very important to be able to tell when answering a subject that modulates, in which of its two possible aspects any note is to be regarded. The only notes with which any difficulty is likely to be found are the third and the seventh of the tonic, which are also the sixth and third of the dominant. An examination of the fugues of the great masters will guide us in laying down definite rules for the treatment of both these notes.

128. As we have to regard every note in its relation to the new key as early as possible, the third should be considered as the sixth of the dominant, and answered by the sixth of the tonic, as in our examples to §§ 120, 124, and 125 (a), excepting, 1st, when it comes between other notes of the tonic chord, or is followed immediately by the tonic; and 2nd, when the subsequent appearance of the subdominant in the subject shows that the modulation cannot yet have taken place. The following passage shows the third in both aspects—

J. S. Bach. Cantata, "Lobe den Herren, den mächtigen König."

The F's in the second bar of the subject prevent our regarding it as in the key of G; but at (a) the change is made at the earliest