This lesson is from Music Theory Level 9.  You can see all of the Music Theory courses here

Excerpt from Music Theory Level 9



Topic: The Fugue pt. 1

Fugues are contrapuntal constructions, much like canons, but somewhat more complex. Much like a canon, each voice in a fugue begins with a common motif, which in a fugue is called a subject. As the voices enter, they take turns playing the subject until every voice was able to play it exactly once. This section in which the voices take turns playing the subject is called the Exposition of the fugue.

Unlike a canon, in which all voices repeat the canonnic motif exactly, once the fugue subject is played, each voice is able to function completely independently to the others and play whatever the composer chooses, even if unrelated to the subject, so long as doublings are avoided, the number of voices stays consistent, and the texture remains highly polyphonic throughout.

The voices may also return to the subject after the exposition, or play a modification of it. Such modifications may include Transposition, Retroversion (playing the motif backwards), Inversion, (playing the motif with all intervals reversed, essentially upside-down), Fragmentation (playing only a section of the subject), diminution, augmentation, or a combination of the above.

If there exists a long section of the fugue in which the subject is not played, the section is labeled an episode. Sections past the exposition in which the subject occurs are called fugal developments. If a fugue is concluded during an episode, that episode is called the coda.

Some other common fugal devices include:

• Stretto - A section of a fugue in which the subject enters in one voice partway through the subject taking place in another voice.
• Double/Triple/etc. Fugues - Fugues which have two, three, or more subjects undergo exposition and fugal development at the same time.
• Fugato - Oftentimes fugue-like subjects occur in pieces which do not fully follow the formal fugue conventions. For example, such sections may have an inconsistent number of voices or incomplete or incorrect expositions. These sections are labeled fugatos ("little fugues").
• Counter Subject - A counter subject is another motif which often accompanies the subject when it occurs.

Fugues are generally labeled based on the number of voices they use (for example: "three voice fugue", "fugue in 6 voices").

Let us use Bach's B-flat minor fugue from the first book of the Well Tempered Clavier (audio for this lesson). Below is an annotated copy. As the title notes, this is a 5-voice fugue. We have highlighted every entrance of the subject in a different color based on the voice in which it occurs. The colors assigned are, from the top voice to the bottom voice:

1. Yellow

2. Red

3. Blue

4. Green

5. Purple



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