Fugue
In classical music, a fugue is a contrapuntal, polyphonic compositional technique in two or more voices, built on a subject that is introduced at the beginning in imitation, which recurs frequently throughout the course of the composition. It is not to be confused with a fuguing tune, which is a style of song popularized by and mostly limited to early American music and West Gallery music. A fugue usually has three main sections: an exposition, a development, and a final entry that contains the return of the subject in the fugue's tonic key. Fugues can also have episodes, which are parts of the fugue where new material often based on the subject is heard; a stretto, when the fugue's subject overlaps itself in different voices, or a recapitulation. A popular compositional technique in the Baroque era, the fugue was fundamental in showing mastery of harmony and tonality as it presented counterpoint.
In the Middle Ages, the term was widely used to denote any works in canonic style; however, by the Renaissance, it had come to denote specifically imitative works. Since the 17th century, the term fugue has described what is commonly regarded as the most fully developed procedure of imitative counterpoint.
Most fugues open with a short main theme, called the subject, which then sounds successively in each voice. When each voice has completed its entry of the subject, the exposition is complete. This is often followed by a connecting passage, or episode, developed from previously heard material; further "entries" of the subject are then heard in related keys. Episodes and entries are usually alternated until the final entry of the subject, at which point the music has returned to the opening key, or tonic, which is often followed by a coda. Because of the composer's prerogative to decide most structural elements, the fugue is closer to a style of composition rather than a structural form.
The form evolved during the 18th century from several earlier types of contrapuntal compositions, such as imitative ricercars, capriccios, canzonas, and fantasias. The Baroque composer Johann Sebastian Bach, well known for his fugues, shaped his own works after those of Jan Pieterszoon Sweelinck, Johann Jakob Froberger, Johann Pachelbel, Girolamo Frescobaldi, Dieterich Buxtehude and others. With the decline of sophisticated styles at the end of the baroque period, the fugue's central role waned, eventually giving way as sonata form and the symphony orchestra rose to a more prominent position. Nevertheless, composers continued to write and study fugues; they appear in the works of Wolfgang Amadeus Mozart and Ludwig van Beethoven, as well as modern composers such as Dmitri Shostakovich and Paul Hindemith.
Etymology
The English term fugue originated in the 16th century and is derived from the French word fugue or the Italian fuga. This in turn comes from the Latin fuga, which is itself related to both fugere and fugare. The adjectival form is fugal. Variants include fughetta and fugato.Musical outline
A fugue begins with the exposition and is written according to certain rules. The composer has more freedom once the exposition ends, though a logical key structure is usually followed. Further entries of the subject will occur throughout the fugue, repeating the accompanying material at the same time, and often accompanying key changes. The various entries may or may not be separated by episodes or occur in stretto.Exposition
A fugue begins with the exposition of its subject in one of the voices alone in the tonic key. After the statement of the subject, a second voice enters and states the subject with the subject transposed to another key, which is known as the answer. To enable a natural harmonic progression, the answer may also be altered slightly. When the answer is an exact transposition of the subject into the new key, the answer is classified as a real answer; alternatively, if the intervals of the subject are altered in any way, the answer is a tonal answer.When the subject begins with a prominent dominant note, or when there is a prominent dominant note very close to the beginning of the subject, a tonal answer is usually necessary. To prevent an undermining of the fugue's key, this note is transposed up a fourth to the tonic rather than up a fifth to the supertonic. For the same reason, it is possible for the answer of such a subject to be in the subdominant key.
During the answer, the voice in which the subject was previously heard accompanies with new material. If this new material is reused in later statements of the subject, it is called a countersubject; if this accompanying material is only heard once, it is simply referred to as free counterpoint.
File:Interval Inversion.jpg|thumb|400px|The interval of a fifth inverts to a fourth and therefore cannot be employed in invertible counterpoint, without preparation and resolution.
The countersubject is written in invertible counterpoint at the octave or fifteenth. The distinction is made between the use of free counterpoint and regular countersubjects accompanying the fugue subject/answer, because in order for it to be heard accompanying the subject in more than one instance, the countersubject must be capable of sounding correctly when played above or below the subject, and must be conceived, therefore, in invertible counterpoint.
In tonal music, invertible contrapuntal lines must be written according to certain rules, because several intervallic combinations, while acceptable in one orientation, are not permissible when inverted. As an example, perfect fifths are contrapuntally acceptable, while the inversion of a perfect fifth results in a perfect fourth, which, unlike the perfect fifth, is considered a dissonance, requiring proper preparation and resolution. The countersubject, if sounding at the same time as the answer, is transposed to the pitch of the answer. Each voice then responds with its own subject or answer, and further countersubjects or free counterpoint may be heard.
It is customary in the exposition to alternate entrances of the subject with entrances of the answer. However, this order is occasionally varied. For example, the exposition from J.S. Bach's The Well-Tempered Clavier Fugue No. 1 in C Major, BWV 846 uses a SAAS exposition. A brief codetta is often heard connecting the various statements of the subject and answer, smoothly connecting each and often facilitating the modulation between the tonic and the key of the answer. The codetta, like other parts of the exposition, may be reused throughout the remainder of the fugue.
The first answer must occur as soon after the initial statement of the subject as possible; therefore, the first codetta is often absent or very short. In the example shown above of J.S. Bach's Fugue No. 16 in G minor, BWV 861, the first codetta is absent. The subject concludes on the quarter note B of the third beat of the second bar, which harmonizes the opening G of the tonal answer. The later codettas may be considerably longer, and often serve to develop the material heard in the subject/answer and countersubject and possibly introduce ideas heard in the second countersubject or free counterpoint that follows. They may also be present to delay, and therefore heighten the impact of, the reentry of the subject in another voice. Finally, they may be modulatory passages to return the fugue to the tonic.
The exposition usually concludes when all voices have given a statement of the subject or answer. In some fugues, especially those with an odd number of voices, the exposition will end with a redundant entry, or an extra presentation of the theme in a voice which has already entered. Furthermore, the entry of one of the voices may not be heard until considerably later. For example, in J.S. Bach's Fugue in C minor for Organ, BWV 549, the subject entrance in the lowest voice, is not heard until near the end of the fugue.
Episode
Further entries of the subject may follow the initial exposition either immediately or separated by episodes. Episodic material is always modulatory and is usually based upon some musical idea heard in the exposition. Each episode has the primary function of transitioning into a new key for the next entry of the subject, and may also provide release from the strictness of form required by the exposition. André Gedalge, a teacher of Maurice Ravel, stated that the episode of the fugue is generally based on a series of imitations of the subject that have been fragmented.Development
Further entries of the subject, or middle entries, occur throughout the fugue. The development must state the subject or answer at least once in its entirety, and may also be heard in combination with any countersubjects from the exposition, new countersubjects, free counterpoint, or any of these in combination. It is uncommon for the subject to enter alone in a single voice in the middle entries; rather, it is usually heard with at least one of the countersubjects and/or other free contrapuntal accompaniments.Middle entries tend to occur at keys other than the tonic. These are often closely related keys such as the relative dominant and subdominant, although the key structure of fugues varies greatly. In the fugues of J.S. Bach, the first middle entry occurs most often in the relative major or minor of the work's overall key, and is followed by an entry in the dominant of the relative major or minor when the fugue's subject requires a tonal answer. In the fugues of earlier composers, middle entries in keys other than the tonic and dominant tend to be the exception, and non-modulation the norm. One famous example of such non-modulating fugue occurs in Buxtehude's Praeludium in C, BuxWV 137.
When there is no entrance of the subject and answer material, the composer can develop the subject by altering it. This is called a counter-exposition, which often uses the inversion of the subject, although the term is sometimes used synonymously with middle entry and may also describe the exposition of completely new subjects, such as those encountered in [|double fugues]. In any of the entries within a fugue, the subject may be altered by inversion, retrograde, diminution, augmentation, or any combination thereof.