Fugue Musical Form Explained: Basic Structure of a Fugue

A fugue is a multi-voice musical form that hinges on counterpoint between voices. Composers can write fugues for a single instrument (most notably a piano or other keyboard instrument), or they can write them for several individual players.

Johann Sebastian Bach composed some of the greatest fugues in music history during the Baroque period of classical music. Bach composed fugues to both demonstrate the possibilities of contrapuntal composition and showcase the capabilities of the piano, which was a new instrument in his era.

In today's music schools and conservatories, music composition students may compose original fugues as part of their study of counterpoint, polyphony, and traditional music theory and harmony.

The word fugue comes from the Latin and the Italian fuga, and it approximately means "to chase."

• Origin in Medieval era: The fugue structure derives from a Medieval musical tradition called the canon, where one instrument's melody is repeated by another instrument beginning a few beats behind; one melody of a canon is always "chasing" another.
• Rise during Renaissance era: Fugal composition came into its own during the Renaissance era, particularly in the compositions of Italian composer Giovanni Pierluigi da Palestrina. Palestrina, as well as Dutch composer Jan Pieterszoon Sweelinck and German composers Johann Jakob Froberger and Dieterich Buxtehude, composed some of the early fugues that would help define the form.
• Peak during Baroque era: It was during the Baroque era that composers, most notably J.S. Bach, adopted the fugue as an essential form of contrapuntal composition. Through Bach's examples, and through music theory texts like Johann Joseph Fux's Gradus Ad Parnassum, the rules of fugal writing would evolve into their current form.
• Legacy: Nearly all prominent classical composers, from Wolfgang Amadeus Mozart to Ludwig van Beethoven to countless Romantic, Modern, and Postmodern composers have composed fugues as part of their musical portfolios. Yet to this day, the form is most associated with Baroque composers like Bach and George Frideric Handel.

A traditional fugue follows a specific structure, with each section serving a particular harmonic role.

1. 1. Subject: The opening of a fugue is known as its exposition. A fugue exposition begins with the introduction of its central melody, the subject. The subject is the primary motif of the entire fugue and will be the template for other melodies. Any voice in a fugue can play the subject; for instance, in a string quartet, the violins, the viola, or the cello can introduce the subject.
2. 2. Answer: The subject is then followed by an answer, which is a near-exact copy of the subject that is played by a different voice in either the dominant or subdominant key. (For instance, if the first voice plays the fugue's subject in C major, the second voice would play the answer in the key of either F major or G major.) If an answer contains the exact same melody as the subject (just played in a different key), it is known as a "real answer." If the answer is slightly altered to account for the new key, it is called a "tonal answer." The answer can be contrapuntally accompanied by a new melody called the countersubject.
3. 3. Episodes: After establishing a subject, an answer, and a countersubject that accompanies the answer, a composer can move on to episodes. These musical passages are not based on the subject of the fugue, and they do not last very long. Many episodes function to modulate between different keys. A fugue set in C major may first explore closely related keys like G major and A minor before pushing onward to more distant keys like G minor and even C minor.
4. 4. Additional subject entries: Over the course of a fugue, a subject re-emerges many times and in a wage range of keys, thanks to modulation. Subjects can be manipulated through retrograde, inversion, augmentation, and diminution. These various subject entries always come with contrapuntal accompaniment. For instance, if the soprano voice is presenting the subject, the alto, tenor, or bass voices may present a countersubject or an entirely new piece of accompaniment.
5. 5. Stretto: Composers can create greater intensity in a fugue through a stretto section, where subjects are layered on top of each other, almost like a canon, and new subject entries (and their accompaniment) pop up before current subject entries are finished. Stretto sections tend to come near the end of the fugue as it builds toward a climax.
6. 6. Coda: Many fugues end with a coda, which is musical material designed to close out the composition. The coda of a fugue describes any music that comes after its final subject entry.

Fugal writing can take other forms. A fugato is a type of contrapuntal composition that mimics a fugue but does not fully follow the structure. On the other end of the equation, a double fugue is a fugue with two distinct subjects. Some piano sonatas, concertos, and compositions for string quartets contain fugue sections within a larger compositional structure.

The most enduring examples of fugues were written by J.S. Bach during the Baroque period of classical music. Bach, along with Handel, Mozart, Haydn, and Beethoven, created fugal compositions that remain widely studied and performed to this day. Here are some particularly well-known fugues and fugue collections:

1. 1. The Well-Tempered Clavier: J.S. Bach wrote a series of preludes and fugues to demonstrate the capabilities of a clavier (an early piano) tuned with equal temperament—which was a novel concept in the eighteenth century. Bach's two-volume Well-Tempered Clavier lives on not so much as a treatise on piano tuning but as some of the finest fugal writing in classical music.
2. 2. The Art of the Fugue: Later in his career, Bach returned to demonstrations of fugal counterpoint. Bach left The Art of the Fugue unfinished, but it features 14 fugues and four canons that show Bach's contrapuntal experimentation very late in his career.
3. 3. Mass in C minor, K. 139 "Waisenhaus": This mass, composed by Wolfgang Amadeus Mozart, brings fugal writing to a choral context. Although the mass is officially in a minor key, Mozart's frequent modulations keep most of the music in major keys.
4. 4. Hammerklavier sonata: This piano sonata by Ludwig van Beethoven is rarely performed due to its difficulty, but it contains a fugue in the grand finale.

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