syncopations, we have carefully contrasted the countersubject with the subject. At (a) will be seen the interval of a perfect fifth between the two voices. This is generally forbidden in two-part double counterpoint; it is possible here because its inversion, the perfect fourth (see (c) in the seventh bar), can be used as an accented auxiliary note.
195. We have considered the subject as ending on D, in the second bar. This necessitates a codetta (§ 189), which is imitated by each of the following voices. This is a case of very common occurrence. It would have been possible here to consider the subject as extending to the beginning of the third bar. In this case, the answer would have been tonal; we regard the subject as ending on the tonic, so as to illustrate the employment of the codetta.
196. On the entry of the bass with the subject, the alto, which had the answer, takes the countersubject, and the counterpoint of the treble is free. Little difficulty will be experienced in adding the free parts to the subject and countersubject by any student who has mastered Chapter VII. of Double Counterpoint.
197. The exposition might end at (b); but we have introduced the additional entry spoken of in § 186, to show the countersubject below as well as above the subject. This entry is made by the voice that began; but as this is a three-part fugue, it will be seen that the treble, which before had the subject, now has the answer. Notice also at (b) the rest before the entry in the treble. It is generally advisable, though not absolutely necessary, to let a rest precede the re-entry of the subject or answer.
198. The student should now take the subjects given at the end of Chapter IV., and write expositions on them in three parts. He will do well to write two or three expositions at least on the same subject, with different countersubjects, and altering each time the order of entry of the voices. He will be surprised to find how much variety he can obtain by this means in the treatment of the same subject.
199. In the exposition of a four-part fugue much greater variety is possible in the order of entry than with only three parts. But, for reasons already given (§§ 180–182), only a few of the possible twenty-four changes in the order are in actual use. It is doubtful whether, except in the cases of the irregular expositions, to be noticed later in this chapter, any instance can be found of an answer being given by the tenor to a subject announced in the treble, or by the alto to a subject announced in the bass. In consequence of the difference of pitch between the two pairs of voices, the answer should always be given by a voice of the other pair from that to which the voice belonged which had the subject. We said above, that it was generally best, especially in a four-part fugue, that the last entry be in an outer part.
