(con't from Part XXXIX)
By way of review, when we've decided to write an organ fugue, and we've settled upon standard 4 voice texture (SATB) -- and the individual voice entries in the exposition are to proceed in the same order (i.e. firstly soprano, then alto, tenor, and lastly bass) -- and there is to be at least one countersubject maintained throughout -- we find that same countersubject trailing every entry of the subject; this is shown in the vertical columns of this diagram (photo), with blue-colored squares representing the subject and cyan-colored squares representing the countersubject.
Upon the entry of the 3rd voice (tenor) there will be additional contrapuntal material (green) appearing in the original (soprano) voice.
If this same new contrapuntal material in the soprano is maintained in the alto during the 4th entry, and it can be continued in every subsequent entry, then it becomes a 2nd countersubject (with the original countersubject becoming the 1st); if any of these 3 moving lines may then serve as a bass for the other 2 and still make agreeable vertical harmony at every point, then the music is being written in triple counterpoint.
When the 4th voice (bass) enters, another contrapuntal line (green) will appear in the 1st voice (soprano); if this new line can be maintained throughout each subsequent entry of the subject, then it becomes a 3rd countersubject; if any of these 4 lines can then serve as a bass for the others and still make agreeable vertical harmony at every point, then the music is being written in quadruple counterpoint.
What this diagram does not show is that there are also other principles in force in fugue writing which have been distilled from the common practices of composers working over a very long period of time [See blog, Getting Started With Writing, Part XX].
Let us say that, after having become familiar with these general principles and how to apply them, we come across a fugue exposition written by someone else; we are now in a position to evaluate it according to what is good about it, what may be particularly good about it, and what about it, if anything, could stand improvement.
We know that every good fugue must begin with a good subject, and, let us say, the subject in question is indeed a good one and that it happens to be in a minor key (say c minor); the composer can be congratulated here, as not every theme makes a good subject for a fugue; we take special note of which scale degree the subject starts on and whether or not it leaps; we need to know this in order to arrive at a correct answer because the beginning and ending pitch of the subject is important in determining whether the answer will be real or tonal.
Next, we listen for the answer and, let us say, it is real and enters in the dominant (g minor) on the correct note as determined by the subject's starting note; we would then expect the countersubject heard with it to suggest a harmony in mostly consonant 3rds and 6ths and move complimentary to the melodic curve and rhythm of the subject -- that is to say, when a note of the subject is stationary, the countersubject should be moving -- and when the melodic curve of the subject goes up, the curve of the countersubject should go down and vice versa, preferably moving in contrary motion with the subject where possible (this is a general statement only, as there are numerous examples where the composer has incorporated all 3 types of melodic motion -- contrary, oblique, and similar -- into the outline of the countersubject with very satisfactory results).
Let us say however, that we notice a place where the countersubject is standing still when the subject is also standing still; and let us say we also find both of these lines coming to a stop just before the 3rd entry -- and that we also find a place where both the answer and countersubject share the same rhythm and articulation through several consecutive beats.
In such places the energy level drops, and, while composers are certainly free to write, shape, and package their music in any manner they see fit, it can be argued, for good and sufficient reasons using J.S. Bach as authority, that further improvements could be made in this passage to increase the motion and energy of the moving lines and raise interest.
It should be recalled that when the answer enters in the dominant key, this key, like every other key, possesses its own leading tone (7th scale degree) which is different from the home key's leading tone.
This means that, as long as the music remains in this dominant tonality during the 2nd entry, the ear will not sense any pull toward the home key.
Let us also say that, at the conclusion of the answer, no modulating link (interlude, codetta, bridge) reestablishing the home key appears in the score -- that is to say, there is no chromatic inflection (raised 3rd) in the dominant tonality which restores the leading tone (7th degree) of the home key.
When the home key is minor (c minor in this case), then without hearing that raised 3rd (G Major tonality) at the conclusion of the answer the music lacks that sense of magnetic pull back to c minor which the leading tone on the note B provides.
The harmony of this raised 3rd can be and is sometimes implied in the minor key by outlining the root, 5th, and 7th of the dominant 7th chord (in this case, G-D-F) in the melodic motion just prior to the 3rd entry.
Typically however, unless the composer is taking a deliberately bold path which purposely deviates from accepted norms, the return to the home key (c minor) after the 2nd entry should be made as unambiguous as possible.
This is done either by inserting a raised 3rd in the dominant tonality at the conclusion of the 2nd entry (which restores the home key's leading tone) or by creating 2-voice melodic motion which implies it.
Here again, using J.S. Bach as authority, this is perhaps something which the fugue writer working without it might wish to rethink (this would NOT be a concern when the home key is Major since the 3rd of the dominant chord in such a case already has the required major 3rd).
Let us also say that we find the melodic motion of all 3 voices coming to a stop right before the 4th entry; here, once again, the energy level drops which is something to be avoided.
Whenever a passage written in fugal style like this, usually an exposition, is inserted into a primarily non-fugal composition, this is defined as a fugato; some fugatos also incorporate a development in fugal style before concluding.
While certain composers may refer to a fugato they've written into a larger work as a "fugue," this latter designation is reserved for a longer piece which, while it may be found paired with another work or two (a prelude, toccata, chorale, introduction, fantasia, etc.), it can stand by itself as a completed composition.
Keeping these things in mind will permit the organ scholar to better identify elements of superior workmanship in any music written in fugal style as well as help determine what, if anything, could have been done in the final editing to create improvements.
As J.S. Bach learned very early in his life as a musician, studying the work of other composers at times becomes an exercise like this which can pay big dividends to the emerging composer.