170. If, on the other hand, the countersubject begins before the modulation has taken place, it will often need modification similar to that of a tonal answer, according to whether it is accompanying the subject or the answer.
J. S. Bach. Wohltemperirtes Clavier, Fugue 7.
![\new ChoirStaff << \override Score.BarNumber #'break-visibility = #'#(#f #f #f) \override Score.Rest #'style = #'classical
\new Staff \relative b' { \key ees \major \time 4/4 \mark \markup \tiny { (\italic"a") }
\[ bes16^"S" g f g ees aes g aes c8 bes r a16 f |
ees'8 d c4\trill bes16[ \] f' d bes] aes f' d aes |
g8[ \[ aes'^"CS" g f] ees16 c d ees f4 ~ |
f16 ees f g aes f bes, aes' g8 \] \bar "||" }
\new Staff \relative e' { \key ees \major R1*2
\[ ees16^"A" d c d bes ees d ees g8 f r d16 bes |
aes'8 g f4\trill ees16 \] s } >>](http://upload.wikimedia.org/score/i/x/ixru5vhk4hw0kd2ju76im4aksuvbrwd/ixru5vhk.png)
![\new ChoirStaff << \override Score.TimeSignature #'stencil = ##f
\new Staff \relative d'' { \key ees \major \time 4/4 \mark \markup \tiny { (\italic"b") }
s8 \[ des^"CS" c bes aes16 g aes bes c4 ~ |
c16 bes c d ees c f, ees' d8 \] }
\new Staff \relative b { \clef bass \key ees \major
\[ bes16^"S" g f g ees aes g aes c8 bes r a16 f |
ees'8 d c4\trill bes16 \] s } >>](http://upload.wikimedia.org/score/s/n/sn5tu33f4wl8tindq2ny4lh33v3juwd/sn5tu33f.png)
At (a) the countersubject accompanies the answer; at (b) it accompanies the subject itself, and the third from C to E becomes a second from A to G. This is because the third in the answer, between F and D, was only a second (between B and A natural) in the subject. The change in the countersubject must be made, like that in the answer, at the point of modulation. Sometimes, also the countersubject is somewhat altered, even with a real answer, as in the fugue in E, referred to in § 165 (see the extract given later in § 269).
171. It may be as well to remind students that, as the countersubject is first heard against the answer only, it must not make with the answer any intervals which would not be allowed in free two-part counterpoint. The laws regulating the employment of these intervals will be found in Double Counterpoint, Chapter V.
172. Though, as a general rule, the countersubject makes its first appearance as an accompaniment to the answer in the exposition, we not infrequently meet with fugues in which its first appearance is deferred. The great fugue in C sharp minor (No. 4 of the 'Wohltemperirtes Clavier') is an example of this kind. We have already quoted the subject and answer in § 66. The counterpoint against the answer seen in that example accompanies also the entry of the third voice, but not those of the
