(con't from Part XXIII)
Instead of pairing a fugue with a prelude, toccata, praeludium (multi-sectional north German toccata), choral, or fantasia, we might choose to write something different ... maybe nothing more than a passage in free form using imitations which we might entitle "Introduction."
As its name implies, this is a passage preliminary to the main part of the work -- a section which often functions to hint at certain motifs or other thematic material in advance of the music which follows it.
When the following fugue has 2 countersubjects, one of the ways we can do this is to write a section that introduces only the first 2 bars of both countersubjects and a variation of the subject derived by rhythmic transformation, pass this material through all near keys in no particular order, and end this portion of the work on a half cadence which leaves an impression of incompleteness.
An example of this type of treatment is the Op. 20 Introduction and Fugue in G Major (photo).
The Introduction of this work was conceived as improvisory in nature where the music is in free form; the rhythm here could also be free, but because it was decided that this section would consist of a 3 voice passage of quiet polyphony where, once all 3 lines begin, they would continue uninterrupted, it was also decided to keep a steady rhythm.
We recall Bach's "great" Toccata in d minor [See blog, Bach d minor, Parts I, II, III, IV, V], where we have free form, structure within parameters, but the rhythm is entirely free where we don't necessarily have to count beats.
Here, we don't have a free rhythm, just free form where there's a steady beat.
Also, with most improvisations, the effort is made to make it sound written; in this case, it's the other way around: this is a written work with all effort being made to make it sound like an improvisation.
Definitely different. And unexpected.
It will help to print a hard copy of this score and follow it along with this narrative; the Fugue is discussed separately in a different posting [See blog, Getting Started With Writing, Part XIX].
The first 2 bars of the Fugue's subject were subjected to rhythmic transformation (same notes in consecutive order, different values) to derive the main theme, or subject, used in the introduction (abbreviated "Sub"), which begins as a single line in the bass in the tonic key (G).
The Sub then enters in imitation in the tenor line, creating a 2nd moving line; the 3rd line then enters in imitation with the Sub in the soprano to complete a 3 part (trio) texture which is maintained throughout this section of the work save for the final 3 measures of the Introduction, where a 4th voice is added.
A cadence in the relative key (e minor) completes the first 11 bars, at which time the first 2 bars of the fugue's 1st countersubject (abbreviated "1st CSub) begin in the tenor line.
Shortly thereafter the 1st half of the fugue's 2nd countersubject (abbreviated "2nd CSub") then enters in imitation in the bass, with another cadence in e minor.
A modulation of 2 bars lands the music in the dominant key (D) where 1st CSub enters in the bass line immediately followed by the Sub, also in the bass.
Two bars later the music modulates to the subdominant key (C) where the 1st CSub enters in the tenor line as the 2nd CSub enters in the bass with some of its notes shifted to a different octave for better voice leading.
Two bars after this, the music remains in the key of C, but the 1st CSub enters in the soprano line and the 2nd CSub enters in the tenor, again with some of its notes shifted to a different octave.
The music quickly modulates to the subdominant relative key (a minor) where the 2nd CSub enters in the tenor.
This is followed by the 1st CSub entering in the tenor line as the 2nd CSub enters in the soprano; the Sub then enters in the soprano line.
The music then modulates to the dominant relative key (b minor) where the Sub enters in the soprano line and the 2nd CSub enters in the bass.
The music then modulates back to the tonic key (G) where a fragment of the 1st CSub enters in the tenor and the 2nd CSub enters in the soprano with some of its notes shifted to a different octave.
Having passed through all (5) near keys, the music then comes to rest on a 4 voice dominant chord in the key of D, creating a half cadence.
It's important to remember, when we're approaching a half cadence like this in the key of G, to keep all C's natural, not sharp, so that when the music comes to rest on a D Major chord it sounds like a dominant chord, not a tonic chord sounding with finality.
If we make every C sharp in the closing measures, the new key of D Major will be suggested, and that same final chord will sound like a new tonic instead of the dominant; if this should be allowed to happen, then the effect of the half cadence, which is supposed to leave an impression of incompleteness, will be lost.
It sounds unnecessary to mention, but it's an easy mistake to make; it's an oversight; we're rolling right along with our writing in what looks like the key of D Major, and oops, we discover we've goofed and have to go back and get rid of all those C#'s and turn them into C naturals to stay in the key of G!
The same situation is encountered in the score of Voluntary in G Major Op. 7, as the half cadence is approached at the close of the short introductory section ... same key, too! [See menu bar, Free Stuff].
We also find a half cadence at the close of the 2nd free section in the Praeludium from Praeludium and Fugue in d minor Op. 10, where the same precaution applies [See menu bar, Free Stuff].
The overall impression left by this or any other Introduction so conceived should be a beautiful section of quiet polyphony that almost seems to disappoint when it must come to a stop finally, in that it flows along so evenly that the listener almost wishes it would continue.
As a result of this treatment of the thematic material, by the time the Fugue begins the listener senses a definite family resemblance between the Fugue's subject and the short little main theme from the Introduction; the first part of the Fugue's 2 countersubjects are also readily recognizable, and all this amidst a very strong sense of unity between the Introduction and the Fugue.
There are many other possible treatments and forms that could be worked as an imitative passage which introduces a fugue, and the plan worked here is only one of many, many options.
As to the form such an introduction will have, what it's thematic material will be, how this material will be developed, how many voices there will be, and the various twists and turns the music will make until it comes to a stop, the sky seems to be the only limit here (and perhaps the writer's own imagination).
(con't in Part XXV)