Page:Fugue by Ebenezer Prout.djvu/69

Chap. IV.] would have answered it by B, the third of G; but he regards it as the sixth of G, and therefore answers it by A, the sixth of C. When a subject modulates to the key of the dominant, all that part which is in the tonic key is transposed in the answer a fifth higher, or a fourth lower; and that part which is in the key of the dominant is transposed a fourth higher, or a fifth lower.

121. The next question is, when there is a modulation, at what point are we to consider it as taking place? The general practice of the great composers is to regard the modulation as being made at the earliest possible point, and from that point to consider every note in its relation to the new key.

122. That the student may quite clearly understand what is meant by this, we will take all the notes in the scale of C major, and show how each can be correctly answered in two ways, according to the point of view from which it is looked at. Supposing our fugue to be in the key of C, and that a modulation to the dominant occurs in the subject, the answer to each note will depend on whether that note comes before or after the modulation:—

"C, if regarded as tonic of C, will be answered by G; but if regarded as the subdominant of G, it will be answered by F, the subdominant of C.

D, as the supertonic of C, will be answered by A, the supertonic of G; but D, as the dominant of G, will be answered by G, the dominant of C.

Similarly E, as the third of C is answered by B, the third of G; but if considered as the sixth of G (as in the example in § 120), it will be answered by A, the sixth of C.

F, the subdominant of C, is answered by C; but, as the minor seventh of G, it will be answered by B flat.

G is answered by D when it appears as a dominant, and by C when it is treated as a tonic.

A as a submediant is answered by E, and as a supertonic by D.

B, the leading note of C, is answered by F sharp; but if the context shows it to be the major third of G, it will be answered by E, the major third of C."

123. If the student clearly understands this possible double relation of every note it will save him an infinity of trouble in making a correct tonal answer. We will now analyze a few short examples illustrating the principle just laid down that the modulation should be considered as taking place as early as possible.

124. As an extremely simple example, we will first take the short passage by Mozart, already quoted in § 57—