answer will therefore be in the key of the dominant; and, except the first note of the second bar, every note of the subject belonging to the key of E flat must be answered by the corresponding note of the key of B flat. It must be especially noticed that though the note B flat (the dominant of E flat) is used four times in the course of the subject, it is answered every time except the first by F, and not by the tonic, E flat. The rule of answering tonic by dominant, and dominant by tonic, applies only to the beginning of a subject and to passages where a modulation to the dominant occurs. In the present case the claims of the law are satisfied as soon as E–B at the beginning of a subject has been answered by B–E; after this, the rest of the subject is transposed, as if the answer were real, into the key of the dominant. The following notes of the subject are respectively the subdominant, mediant, submediant, and dominant of E flat; and they are answered by the subdominant, mediant, submediant, and dominant of B flat—and so on, to the end of the answer. There is no mistake which students are more apt to make in beginning to write tonal answers than to answer dominant by tonic every time these notes occur. This is almost invariably wrong.
89. If we look at the second bar of the above example, we shall find that an interval of a second in the subject has become a unison in the answer. Whenever a subject begins with the leap from tonic to dominant, it always, if answered tonally, causes a change in the following interval. Here the first and third notes of the subject are the tonic and subdominant of the tonic key; the first and third notes of the answer are the tonic and subdominant of the dominant key: but the difference in the size of the first leap of the subject (a fifth), as compared with the leap of a fourth in the answer, makes a difference also in the interval between the second and third notes. We give two more illustrations of the same point—
J. S. Bach.
Wohltemperirtes Clavier, Fugue 17.
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\cadenzaOn dis4^\markup \bold "S" ais'4. b8[ ais gis] \bar "|"
fis[ gis] ais4 dis, gis ~ \bar "|" gis8[ fis] eis4 dis4. }
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\cadenzaOn ais4^\markup \bold "A" dis ~ \bar "|"
dis8[ fis eis dis] cis[ dis] eis4 \bar "|"
ais, dis ~ dis8[ cis] bis4 \bar "|" ais8 s4 } >> }](http://upload.wikimedia.org/score/m/2/m2q745a86oc4plm22smas38sk2kon3s/m2q745a8.png)
At (a) a third in the subject becomes a second in the answer; at (b) a second in the subject becomes a third in the answer. Note,
