# Fugue (Prout)/Chapter 12

CHAPTER XII.
THE FUGUE ON A CHORAL.
415. In addition to the different varieties of fugues treated of in the preceding chapters, we not infrequently find fugues written upon a choral. As with a canon on a choral (Double Counterpoint, § 391), there are two ways in which this can be done. We can either take the melodies of the choral itself as the subjects of our fugue, or we can write a fugue on an entirely independent subject, introducing the choral in longer notes in one of the voices as a kind of canto fermo. Owing to the much greater freedom of its form, it is far easier to write a fugue on a choral than a canon.
416. We will first speak of that form in which the choral itself furnishes the subjects of the fugue. The plan most often followed is to write a separate fugal exposition for each line of the choral, the last entering voice, which, for the sake of clearness, is generally one of the outer parts, introducing the melody, in most cases, though not invariably, by augmentation.
417. As this method will be best taught by examples, we give two entire fugues of this kind, one very simple, the other rather more elaborate. The first is by one of Bach's great predecessors, the Danish organist Buxtehude. It is on the choral "Erhalt uns, Herr, bei deinem Wort." In the original there is only one flat in the signature, according to the custom of the time, though the key of the piece is G minor; for the convenience of students, we adopt the modern key-signature.
Buxtehude.
418. The first line of the choral is announced as a fugue subject in the tenor, and answered by the alto in bar 3. The treble gives the subject again in bar 6, and the bass (pedals) joins in with the subject at bar 8. The subject, and not the answer, is given to the bass, because, as we see from the rest of the fugue, this part has the character of a canto fermo, and gives nothing but the simple choral, line by line, throughout the piece. We therefore find the subject here instead of the answer, as in an ordinary fugal exposition. It will be seen that the canto fermo is here only in notes of the same length as the other parts. More usually, as in our next example, the plain choral is given in longer notes.
419. At bar 10 begins the exposition of the second line of the choral. Here we see a little irregularity of treatment. The theme in an ornamented form appears in the tenor, and is imitated in stretto in the next bar by the treble. At bar 13, the answer is repeated, not by the alto (which had not had it), ​but by the tenor which gave the subject just before. The entry of the subject in the bass (bar 16) concludes the second section of the fugue.
420. The third section is longer. The subject is first heard in the alto (bars 18 to 20), the answer in the treble (bar 21), and again in the tenor (bar 23), followed by an additional entry of the subject in the alto (bar 26), and completed by the canto fermo on the pedals (bars 28 to 30). The treatment of the last line is on a similar plan, as the student will easily see for himself.
421. It will be noticed that this fugue really consists of four short expositions of different subjects, but that the first entries in all the lines of the choral, except the first, are accompanied by independent counterpoint. It is not necessary that all the intermediate expositions in a fugue on a choral should begin with one voice alone, though our next example will show that this may sometimes be done.
422. The above fugue is given not as a perfect model for imitation, but as showing one of the earlier and simpler ways of treating a choral in the fugued style. The following example by Bach is a much more finished and artistic piece of work.
J. S. Bach, "Vom Himmel hoch da komm' ich her."
​ ​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 ​lines of the choral as a canto fermo at such points as may be found most convenient. A fugue of this kind is very seldom strict as to the intervals of entry. Of the numerous specimens to be found in Bach's 190 Church Cantatas, there is not a single one which would not be more accurately described as a fugato with a choral. As these have nearly always an independent orchestral accompaniment, we prefer to select as an illustration the first twenty bars of a fugue on a choral taken from one of the motetts. The movement is too long to be quoted in full.
J. S. Bach. Motett, "Fürchte dich nicht."
​ ​428. Here the key of the piece is A major; the subject, therefore, being throughout in the dominant, the answer is in the tonic (§ 70). The first answer is at the regular interval; but the next entry of the subject (bar 4) is in the key of D instead of E; and from this point the entries, though each is generally at a fourth or fifth above or below the preceding, are so irregular that it is impossible to say which are subjects, and which are answers. We have therefore marked them all with 'S.'
429. It must be remembered that it is not allowed to transpose any phrases of the canto fermo into other keys; consequently only such modulations are available as can be introduced without doing violence to the original form of the choral. The same rule, of course, applies to the variety of fugue noticed in the earlier part of this chapter. Any other modulations, if used at all, can only be employed in what may be termed the interludes between the different lines of the choral. For instance, in our last example is a transient modulation at bar 9 to the key of E minor, introduced between the first and second lines of the choral.
430. Though it is advisable, where practicable, to employ the theme of the fugue as a counterpoint against the choral, it is also allowed to introduce the latter during the episodes. This considerably lightens the composer's labours; for (as we have already seen in Chapter VII.), though the materials of the episodes should have some connection with the subject or countersubject of the fugue, considerable liberty of treatment is allowed; and it will be much easier to introduce the choral than if we are bound to make it combine with a given theme.
431. A fine example of this method of treatment is seen in Mendelssohn's third Organ Sonata. There is here a double fugue, each subject having a separate exposition before they are combined. We quoted the first subject in § 38 (d). After a regular four-voice exposition, Mendelssohn at the 17th bar of the fugue introduces on the pedals the first line of the choral "Aus tiefer Noth schrei 'ich zu Dir," as a fifth part. The subject is only suggested above the choral, a new entry taking place on the last notes of the line. The entries of the second and third lines of the choral (bars 22 and 28) are similarly treated. At bar 35 the exposition of the second subject (a figure of semiquavers) begins. After it has been carried through all the voices there is an episode (bars 43 to 47) against the latter half of which (from bar 45) the next line of the choral is heard. At bar 57 the two subjects are combined, and the choral is introduced in the pedals from time to time; but in no one place throughout the fugue is either of the subjects in its entirety ever combined with the choral.
432. Mendelssohn's organ sonatas are so well known and so accessible that we have contented ourselves with merely referring to this fugue instead of quoting from it, because no short extracts from it would have been of much assistance to the student. It ​shows that it is not necessary actually to combine the fugue subjects with the choral. This fugue is a very fine specimen of its class, and it is no disparagement to Mendelssohn's genius that he has here preferred the freer style. It would have been very difficult (perhaps impossible for anyone except Bach, to whom nothing seems to have been impossible) to combine the choral with either of the themes he had selected for his fugue. He therefore wisely chose rather to write an effective composition than to attempt elaborate and difficult combinations, which, had he succeeded in effecting them, would probably have smelt strongly of the lamp. An over-display of technical cleverness is very likely to be dry.
433. Sometimes only the first line of a choral, instead of the whole, is selected for fugal treatment. A well-known example of this is Bach's organ fugue in E flat, known in England as the 'St. Ann's Fugue.' This is a double fugue of a somewhat unusual form, in three movements. The first is a simple fugue in five parts, the theme of which we quoted at § 102 (c), and which is the same as the first line of the hymn-tune, 'St. Ann's.' This movement ends with a full cadence in the tonic, introducing the second subject.
J. S. Bach. Organ Fugue in E flat, ('St. Ann's.')
This second movement is in four parts only, without pedals. After a regular exposition, the new subject is treated by inversion, and then combined with the first subject, of which the rhythm is now altered, and which assumes the character of a canto fermo.
Subsequently the canto is also heard against the inversion of the second subject. A full close in C minor leads to the third movement, which, like the first, is in five parts. The theme will be seen at § 49 (c). We now have a third exposition, followed by combinations of the third subject with the canto fermo in various ways, of. which one will serve as a sample.
It must be noticed that, though this fugue contains three subjects and three expositions, like the great fugue analyzed in Chapter XI., §§ 400–402, yet it is not really a triple fugue, as the three subjects are never all heard together. It more nearly resembles a fugue with two countersubjects heard in succession (§ 174).
434. The fugue on a choral affords an illustration of the general principle so often referred to in these volumes, that in proportion as the difficulty of the task increases, greater freedom is allowed to the composer. This has been amply shown in our examples. By the time that the student is so far advanced as to be able to attempt a composition of this class, he ought also to have acquired sufficient experience not to permit his liberty to degenerate into license.