74. Now let us examine the answer. The first note is C. This cannot be regarded as a subdominant, because the tonic at the commencement of a subject cannot be answered by a subdominant. We have already seen that it is almost invariably answered by dominant—that is to say, by the tonic of the key in which the answer appears. The C here must therefore be considered not as the subdominant of G minor, but as the tonic of C minor. This choice of a key for the answer enables Bach to carry out the important general principal already mentioned, and of which we shall have more to say when we come to speak of tonal answers, that dominant harmony in the subject should be replied to by tonic harmony in the answer. Here we have the dominant seventh chord in G at the first bar of the subject, answered by the notes of the tonic seventh of G in the first bar of the answer. It would have been quite possible to give a real answer for this bar, beginning on the dominant; but then the dominant harmony of the subject would have been answered by the supertonic harmony, instead of the tonic.
75. It will also be seen that at the second bar of the subject there is a modulation to the dominant key. Such a modulation is almost invariably answered by a return to the tonic key. Here, however, the tonic harmony in the answer is really the harmony of the dominant key of C minor. Had the answer not been in the key of the subdominant, a tonal answer would have been necessary.
76. Our next illustrations, containing no modulation,
