A fugue is a contrapuntal composition for a number of separate parts or voices.
e.g. “a fugue in 4 parts”, “a fugue in 3 voices”.
Each part/voices enters in imitation of each other.
In this music theory lesson we are going to look at the basic structure of a fugue in 4 voices/parts.

The Basic Structure of a Fugue

The 1st voice/part starts by playing a melody/phrase called the Subject.
The 2nd voice then enters playing the “answer”. The answer is a transposed version of the subject.
The 3rd voice then enters playing the subject again and then the 4th voice enters playing the answer.
This whole section of music is called The Exposition.
When all the voices have entered this signals the end of the Exposition

After the Exposition there comes an Episode.
This is a connecting passage of music and is usually made up of a development of the music that has already been heard in the Exposition.
After the Episode, there is another entry (or entries) of the Subject, followed by another Episode. This alternating of Subject entries and Episodes continues until the end of the piece.

Diagram of Basic structure of a fugue

Contrasts of Key in a Fugue

Contrasting keys play a vital role in the composition of a fugue.

Key Contrasts in the Exposition

In the Exposition the subject 1st appears in the tonic key.
The 2nd voice plays the “answer” in dominant key (a 5th higher or a 4th lower) – this transposed line in the 2nd voice is called the answer. If it is an exact transposition of the subject then it is called a “real answer”. However, if it is altered to fit the new key then it is a ”tonal answer”.
The Subject is repeated in the entry of the 3rd voice (usually in the tonic, but at a different octave) and is “answered” by the 4th voice, again in the dominant key.

Diagram of key changes in fugue exposition

Key Contrasts in Episodes

The Episodes are often used by the composer of a fugue to modulate to different keys. This brings added variety to the entries of the Subject later on in the fugue.

Other Features of Fugues


A Countersubject often appears in the Exposition (and also later in the fugue). A countersubject acts like an accompaniment to the Subject and Answer. So, the voice/part which has just played the Subject will go on to play the Countersubject whilst the next voice is playing the answer.


Stretto literally means “drawn together”. In the context of a fugue it describes a situation where each voice enters before the previous voice has finished its subject. This overlapping technique is used by composers to increase the emotional tension of the piece.
Here is a diagram of stretto:

Diagram of use of stretto in a fugue

Can you see how each voices enters before the previous voice has finished playing its subject?

Double Fugues

You will sometimes come across Double Fugues. These can be seen in 2 forms:

  1. 2 subjects appear together at the start of the piece
  2. A subject is introduced at the start of the piece and answered in the usual way. A second subject is then introduced and also answered. The 2 subjects are then combined at a later point in the piece.

Example of a double fugue – J.S. Bach – Prelude and double fugue no. 18 in G sharp minor BMV 887 (WTC II)

Other Useful fugal forms

  • Fughetta – this is a shortened fugue
  • Fugato – this is a passage of music in fugal style, but not in itself an actual fugue.
  • Accompanied Fugue – these are sometimes found in oratorio movements where there is a free instrumental part accompanying the singing.

Examples of Fugues

There are many examples of fugues. Arguably the most famous composer of fugues is J.S. Bach. Have a listen to any of Bach’s fugues from the Well Tempered Clavier to get started.
Alternatively, have a listen to this string quartet play The Art of Fugue by Bach.

In Depth Analysis of a Fugue

An in depth analysis of a fugue is beyond the scope of this music theory lesson.
However, if you are wanting to extend your knowledge of fugues here is an excellent analysis of a Bach fugue by an American educator.