Page:Fugue by Ebenezer Prout.djvu/67

Chap. IV.]

114. In our last chapter we showed that a tonal answer, though often advisable, was never absolutely necessary for any subject which did not modulate to the key of the dominant. We have now to deal with the treatment of the answer to subjects in which such a modulation occurs.

115. In order to render intelligible the principles on which we shall have to proceed, it is needful here to anticipate somewhat, and to say that in the exposition (§ 11) of a fugue, only two principal keys are employed—mostly tonic and dominant, occasionally tonic and subdominant. In an enormous majority of cases the keys will be tonic and dominant. We saw in the last chapter that if the subject were in the key of the tonic, and remained in it, the answer would be and remain in the key of the dominant. The third voice will almost invariably enter with the subject, and the fourth, if there be four, with the answer. In such cases the answer will generally be real, or if there be any tonal alteration, it will only affect the first two or three notes of the subject.

116. But now suppose that instead of ending, as it begins, in the tonic key, the subject modulates to and finishes in the dominant, as in the case given at § 57 (b). It is quite Clear that if we give a real answer in this case, the answer will end in the dominant of the dominant, that is, in the key of the supertonic—

Here we have not only introduced a third principal key, where, as was said in the last paragraph, there ought only to be two; but (what is still more objectionable) we have modulated to an unrelated key (Harmony, § 225). To get back to the tonic key for the entry of the third voice, we shall have to introduce an awkward and probably clumsy join by means of a codetta. In order not to wander away into an unrelated key, and to confine ourselves to the two chief keys already mentioned, which will always be at a distance of a fifth apart, we require a tonal answer here, and adhere to the old rule. This is:—If the subject begin in the tonic, and, modulate to the dominant, the answer must begin in the dominant and modulate to the tonic.