423. Here the canto fermo is in the treble, in minims against the crotchets and quavers of the other voices, and the fugue is a close fugue (§ 279). It will be seen that the second and third lines of the choral (bars 6 and 12) are treated in fugato style, the entries not being at the regular intervals, while the first and fourth (bars 1 and 20) are in the intervals of subject and answer. The close imitations, and the treatment of fragments of the subjects deserve careful examination.
424. If we observe the form of these two fugues, we shall find that they both differ considerably from the general fugal form described in Chapter IX. This will always be the case with a fugue on a choral; and it is quite impossible to lay down any fixed rules for its form, because this will in all cases depend on the course of modulations of the choral itself. A certain amount of variety is always obtainable by varying the harmonies of the different lines of the choral, as Bach has done in the above example, by harmonizing the end of the second line of the choral (bars 11 and 12), not as a full cadence in E flat, but as a half cadence in C minor. But in the case of short and simple chorals, such as the two given in our last examples, there will generally be comparatively little modulation, and only to nearly related keys.
425. Another point illustrated by these two fugues is, that the entries of the lines of the choral as a canto fermo need not be at any regular intervals of time. In Buxtehude's fugue, the first line enters at the eighth bar, there are five bars' rest between the first and second lines, nine between the second and third, and nine between the third and fourth. With Bach, there is a bar and a half before the entry of the first line, two bars between the first and second, three between the second and third, and three again between the third and fourth. The points at which the various entries should be made is a matter that is entirely within the composer's discretion; he may introduce his canto fermo exactly where he finds it most convenient.
426. This form of fugue on a choral is less common in modern music than it was in the last century. Two effective examples may be seen in the late Sir George Macfarren's oratorios. The chorus, "My soul, praise the Lord," in 'St. John the Baptist,' is founded on Dr. Croft's hymn-tune 'Hanover'; and the 'Old Hundredth' is treated fugally in the final chorus of 'The Resurrection.' Both these fugues, however, differ from the models here given, inasmuch as, although the whole of the choral is heard as a canto fermo, the actual subject of the fugue itself is in each case only the first line. These pieces, therefore, form a kind of connecting link between the variety already treated of and that now to be described.
427. The second method of writing a fugue upon a choral is to take an entirely independent subject—that is, one not suggested by any part of the choral itself—and against this to introduce the
