The first thing you should do before practicing it is to analyze the structure and tonal plan of this fugue. Since it is a fugue, it has rather strict requirements which Baroque composers usually followed. The fugue is a piece of imitative polyphony in which the composer reveals the possibilities a theme has to offer.
You may be wandering why this fugue is in the key of G minor but only has one flat next to the clef. You see, this is a remnant of the old modal system that Bach still occasionally used. The mode which is built around note of G and has one flat is called “Dorian”. This means we can say this fugue has features of the Dorian mode.
Now look at the theme or subject at the beginning of the fugue. It is 5 measures long. Now try to count the other appearances of the theme in the fugue and label them on your score with a pencil. Look at each voice. Remember that the theme can be not only in the home key of G minor, but in other related keys as well. Write down the names of the keys on the score. This will be the tonal plan of this fugue.
In addition, look especially at the melodic line which appears in the soprano voice after the theme enters in the alto. This is a countersubject. Sometimes composers used different countersubjects with every appearance of the theme. This is not the case with this fugue. Interestingly, this countersubject is constant and Bach uses it with every subject (sometimes a little bit altered).
So the subject and countersubject are the two main building materials of this fugue. Look what happens between subject entrances. These places without a subject are called episodes. The material for them is taken from the theme or the countersubject. Episodes are meant to help modulate from one key to another. One of the easiest ways to achieve that is through sequences. A sequence is melodic or harmonic idea that is repeated in ascending or descending manner and either stays in the same key or modulates to another key. For example, in measures 22-23 we see a descending sequence. Try to count other sequences in this fugue.
Now that you know the basic formal and tonal structure of this composition, you could start practicing it on the organ. I have written earlier about my method I use that will help you to master any organ piece. You could take the same steps while playing this fugue, too.
Subdivide the piece into smaller fragments. These could be of the same length as that of the theme or you could subdivide it according to lines. Always start and finish playing the fragment on the down beat. That way the fragments will be connected with each other.
Write in fingering and pedaling in Fragment 1. Make sure you avoid finger substitutions, placing a thumb on a sharp key (except where there is no other option) and use toes only pedaling. This type of fingering and pedaling helps to achieve the desired articulation for any piece of the Baroque period – the articulate legato or as the contemporary sources called it - the ordinary touch.
This type of articulation means that there should be small breaks between each note. However, the notes should not be too detached. It should be executed in a singing (cantabile) manner.
Additionally, feel the alternation of the strong and week beats in each measure. Articulate a little bit more before beats 1 and 3 in each measure.
Because each voice is very independent, it is best to practice each voice of that fragment separately, then in two-voice combinations, later in three-voice combinations, and finally, all four voices together. Practice slowly and use pedal preparation. Repeat each combination several times until you can play it precisely and without mistakes at least three times in a row. Then take another combination and do the same thing. When you master fragment 1, take fragment 2 and start over.
When you master all separate fragments, start combining them and play in longer episodes. This type of practicing takes some willpower but in the end you will progress much faster.
Note that there are various instances of ornamentation in this fugue. All trills and mordents here should be played from the upper note. In measures 19 and 43 you will see a trill sign over a long note. These trills should be long and played over the entire length of that note, starting from the upper note.
The registration of this piece could be anything from a single 8’ principal up to a full 16’ based principal chorus with pedal reads. Always include a stop of 16’ in the pedals.
Upon learning this fugue, you may find it so beautiful that it would be worthwhile even to memorize it. Refer to my earlier post about memorization. I recommend the New Bach Edition for playing this piece which is solid and quite reliable.
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