Musical improvisation (also known as Musical Extemporization) is the creative activity of immediate ("in the moment") musical composition, which combines performance with communication of emotions and instrumental technique as well as spontaneous response to other musicians.  Thus, musical ideas in improvisation are spontaneous, but may be based on chord changes in classical music.
Because improvisation is a performative act and depends on instrumental technique, improvisation is a skill. There are musicians who have never improvised and other musicians who have devoted their entire lives to improvisation.
Historical development in Western music
Throughout the Medieval, Renaissance, Baroque, Classical, and Romantic periods, improvisation was a highly valued skill. Francesco Landini, Adrian Willaert, Diego Ortiz, Frescobaldi, J.S. Bach, Handel, Mozart, Beethoven, Chopin, Liszt, and many other famous composers and musicians were known especially for their improvisational skills. Improvisation might have played an important role in the monophonic period. The earliest treatises on polyphony, such as the Musica enchiriadis (ninth century), make plain that added parts were improvised for centuries before the first notated examples. However, it was only in the fifteenth century that theorists began making a hard distinction between improvised and written music. Many classical forms contained sections for improvisation, such as the cadenza in concertos, or the preludes to some keyboard suites by Bach and Handel, which consist of elaborations of a progression of chords, which performers are to use as the basis for their improvisation. Handel, Scarlatti, and Bach all belonged to a tradition of solo keyboard improvisation that was not limited to variations, but included the concerto form, typically with moving voices in both hands, occasionally exploring fugue.
Although melodic improvisation was an important factor in European music from the earliest times, the first detailed information on improvisation technique appears in ninth-century treatises instructing singers on how to add another melody to a pre-existent liturgical chant, in a style called organum. Throughout the Middle Ages and Renaissance, improvised counterpoint over a cantus firmus (a practice found both in church music and in popular dance music) constituted a part of every musician's education, and is regarded as the most important kind of unwritten music before the Baroque period.
Following the invention of music printing at the beginning of the sixteenth century, there is more detailed documentation of improvisational practice, in the form of published instruction manuals, mainly in Italy. In addition to improvising counterpoint over a cantus firmus, singers and instrumentalists improvised melodies over ostinato chord patterns, made elaborate embellishments of melodic lines, and invented music extemporaneously without any predetermined schemata. Keyboard players likewise performed extempore, freely formed pieces.
The kinds of improvisation practised during the Renaissance—principally either the embellishing of an existing part or the creation of an entirely new part or parts—continued into the early Baroque, though important modifications were introduced. Ornamentation began to be brought more under the control of composers, in some cases by writing out embellishments, and more broadly by introducing symbols or abbreviations for certain ornamental patterns. Two of the earliest important sources for vocal ornamentation of this sort are Giovanni Battista Bovicelli’s Regole, passaggi di musica (1594), and the preface to Giulio Caccini’s collection, Le nuove musiche (1601/2)
Eighteenth-century manuals make it clear that performers on the flute, oboe, violin, and other melodic instruments were expected not only to ornament previously composed pieces, but also spontaneously to improvise preludes.
Keyboard, lute, and guitar
The pattern of chords in many baroque preludes, for example, can be played on keyboard and guitar over a pedal tone or repeated bass notes. Such progressions can be used in many other structures and contexts, and are still found in Mozart, but most preludes begin with the treble supported by a simple bass. J.S. Bach, for example, was particularly fond of the sound produced by the dominant seventh harmony played over, i.e., suspended against, the tonic pedal tone.
There is little or no Alberti bass in baroque keyboard music, and instead the accompanying hand supports the moving lines mostly by contrasting them with longer note values, which themselves have a melodic shape and are mostly placed in consonant harmony. This polarity can be reversed—another useful technique for improvisation—by changing the longer note values to the right hand and playing moving lines in the left at intervals—or with moving lines in both hands, occasionally. This shift of roles between treble and bass is another definitive characteristic. Finally, in keeping with this polarity, the kind of question and answer which appears in baroque music has the appearance of fugue or canon. This method was a favorite in compositions by Scarlatti and Handel especially at the beginning of a piece, even when not forming a fugue.
Organ improvisation and church music
Improvised accompaniment over a figured bass was a common practice during the Baroque era, and to some extent the following periods. Improvisation remains a feature of organ playing in some church services.
The Classical period
Classical music departs from baroque style in that sometimes several voices may move together as chords involving both hands, to form brief phrases without any passing tones. Though such motifs were used sparingly by Mozart, they were taken up much more liberally by Beethoven and Schubert. Such chords also appeared to some extent in baroque keyboard music, such as the 3rd movement theme in Bach's Italian Concerto. But at that time such a chord often appeared only in one clef at a time, (or one hand on the keyboard) and did not form the independent phrases found more in later music. Adorno mentions this movement of the Italian Concerto as a more flexible, improvisatory form, in comparison to Mozart, suggesting the gradual diminishment of improvisation well before its decline became obvious.
The introductory gesture of "tonic, subdominant, dominant, tonic," however, much like its baroque form, continues to appear at the beginning of high-classical and romantic piano pieces (and much other music) as in Haydn's sonata Hob.16/No. 52 and Beethoven's sonata opus 78.
Beethoven and Mozart cultivated mood markings such as con amore, appassionato, cantabile, and expressivo. In fact, it is perhaps because improvisation is spontaneous that it is akin to the communication of love.
Mozart and Beethoven
Beethoven and Mozart left excellent examples of what their improvisations were like, in the sets of variations and the sonatas which they published, and in their cadenzas. As a keyboard player, Mozart competed at least once with Muzio Clementi. Beethoven won many tough improvisatory battles over such rivals as Johann Nepomuk Hummel, Daniel Steibelt, and Joseph Woelfl.
Extemporization, both in the form of introductions to pieces, and links between pieces, continued to be a feature of keyboard concertising until the early 20th-century. Amongst those who practised such improvisation were Franz Liszt, Felix Mendelssohn, Anton Rubinstein, Paderewski, Percy Grainger and Pachmann. Improvisation in the area of 'art music' seems to have declined with the growth of recording.
After studying something more than 1,200 early Verdi recordings, Will Crutchfield concludes that "the solo cavatina was the most obvious and enduring locus of soloistic discretion in nineteenth-century opera".  He goes on to identify seven main types of vocal improvisation used by opera singers in this repertory :
1. The Verdian “full-stop” cadenza
2. Arias without “full-stop”: ballate, canzoni, and romanze
- 3. Ornamentation of internal cadences
4. Melodic variants (interpolated hight notes, acciaccature, rising two-note "slide")
5. Strophic variation and the problem of the cabaletta
6. Facilitations (puntature, simplification of fioratura, etc.)
Modern opinions on improvisation in art music
Toward the end of the section of Aesthetic Theory entitled "Art Beauty" (in the English edition), Theodor Adorno included a brief argument on improvisation's aesthetic value. Claiming that artworks must have a "thing-character" through which their spiritual content breaks, Adorno pointed out that the thing-character is in question in the improvised, yet present. It may be assumed Adorno meant classical improvisation, not jazz, which he mostly excoriated. He held jazz, for example, to be antithetical to Beethoven. There is more extensive treatment, essentially about traditional jazz, in Prisms and The Jargon of Authenticity.
Improvisation may be pressed to derive something novel from past material, which becomes outmoded through its limited concepts of tonality, form, and variation. Though his understanding of modern music was itself unorthodox, Glenn Gould appears to have such a view as he clearly thought musical history was a finite exploration of forms and tonal concepts, and exhaustible.
Improvisation is one of the basic elements that sets jazz apart from other types of music. Even if improvisation is also found outside of jazz, it may be that no other music relies so much on the art of "composing in the moment", demanding that every musician rise to a certain level of creativity that may put the performer in touch with his or her unconscious as well as conscious states. Many varied scales and their modes can be used in improvisation. They are often not written down in the process, but they help musicians practice the jazz idiom. An example of a musician who improvises on solo piano is Keith Jarrett (see e.g.The Köln Concert).
A common view of what a jazz soloist does could be expressed thus: as the harmonies go by, he selects notes from each chord, out of which he fashions a melody. He is free to embellish by means of passing and neighbor tones, and he may add extensions to the chords, but at all times a good improviser must follow the changes. ... [However], a jazz musician really has several options: he may reflect the chord progression exactly, he may "skim over" the progression and simply elaborate the background harmony, or he may fashion his own voice-leading which may clash at some points with the chords the rhythm section is playing.
Contemporary classical music
While the first half of the twentieth century is marked by an almost total absence of actual improvisation in art music, since the 1950s, some contemporary composers have placed fewer restrictions on the improvising performer, using techniques such as vague notation (for example, indicating only that a certain number of notes must sound within a defined period of time). New Music ensembles formed around improvisation were founded, such as the Scratch Orchestra in England; Musica Elettronica Viva in Italy; Lukas Foss's Improvisation Chamber Ensemble at the University of California, Los Angeles; Larry Austin's New Music Ensemble at the University of California, Davis; the ONCE Group at Ann Arbor; the Sonic Arts Group; and Sonics, the latter three funding themselves through concerts, tours, and grants. Significant pieces include Foss's Time Cycles (1960) and Echoi (1963).
Other composers working with improvisation include Richard Barrett, Pierre Boulez, Cornelius Cardew, Alvin Curran, Stuart Dempster, Hugh Davies, Karlheinz Essl, Vinko Globokar, Richard Grayson, Stephen Nachmanovitch, Pauline Oliveros, Terry Riley, Frederic Rzewski, Karlheinz Stockhausen, Richard Teitelbaum, Christian Wolff, Vangelis, La Monte Young, John Zorn and Yitzhak Yedid.
Several pianists also teach classical improvisation and perform, such as David Dolan, William Goldstein,Yitzhak Yedid and Eric Barnhill.
The 1960's saw The Grateful Dead gain popularity and bring a name to the "jam" genre. Since the 1980's, bands like Phish, Widespread Panic, moe., Umphrey's McGee, and String Cheese Incident have used musical improvisation extensively; indeed, for the more devoted followers of any band, these extended improvisational segments—jams—are a large part of what makes a live show so special. The jam band scene has also seen the rise of "jamgrass" with bands like Hot Buttered Rum, Cornmeal and Yonder Mountain String Band, along with the rise of Livetronica with bands like The Disco Biscuits, Lotus, The New Deal, and STS9 (Sound Tribe Sector 9), most of whom feature improvisation very heavily in their music. There are also bands who play 100% live improvisation Music at their Concerts, making up the standards, patterns, rhythms, melodies, harmonies, lyrics, solos, etc. at the top of their heads. Examples are bands like Xlovers  , and 42winA2 
Silent film music
In the realm of silent film music performance, there are also a small number of musicians whose improvisational work has been recognized as exceptional by critics, scholars and audiences alike: Neil Brand, Guenter A. Buchwald, Philip Carli, Stephen Horne, Donald Sosin, John Sweeney, and Gabriel Thibaudeau, all performers at the annual conference on silent film in Pordenone, Italy, "Le Giornate del Cinema Muto." Their performances have to match the style and pacing of the films they accompany, often at first sight, and demand a knowledge of a wide range of musical styles, as well as the stamina to play for films which occasionally run over three hours in length without a pause. In addition to the performances, these pianists also teach a master class for those who wish to develop their skill in improvising for films.
Pop rock music
Also in pop music musical improvisation is present. Following the structure of previous jazz forms, from the 1950s onwards the most common example of improvisation in pop and rock is the guitar solo. Other instrumental solos, and collective improvisation are also used.
British Psychedelic rock acts of the 1960s and 1970s used improvisations to express the hallucinations of LSD and other drugs in a musical language. Bands like Pink Floyd, Led Zeppelin, Allman Brothers Band, Grateful Dead, The Doors, Velvet Underground, Jimi Hendrix Experience,. The progressive rock genre also began exploring improvisation as a musical expression, Henry CowThe Soft Machine, Robert Fripp, Brian Eno. In the 1980s alternative rock, shoegaze, post rock and similar genres used improvisation. Bands like Spiritualized, Yo La Tengo, Sonic Youth, Mogwai, Explosions in the Sky, Godspeed You! Black Emperor.
Modern electronic instruments or 'groove boxes' allow musicians to perform live sets of endlessly improvised material.
^ Gorow 2002, 212.
^ Gorow 2002, 212.
^ Gorow 2002, 212.
^ Horsely 2001.
^ Horsley 2001.
^ Brown 1976, viii; Fuller 2002.
^ E.g., Ganassi 1535; Ortiz 1553; Dalla Casa 1584.
^ Brown 1976, viii–x.
^ Thomas de Sancta Maria 1565.
^ Collins, Carter, Garden, and Seletsky 2001, (i).
^ Hotteterre 1719.
^ For example, near the beginning of the Toccata of BWV 565. Bach's Cantata BWV 54 also uses this suspension as the opening chord in E-flat Major.
^ For examples of both 'reversed polarity' and 'question and answer' see, e.g., Scarlatti Sonata in A minor K 54
^ Adorno 1997, 221.
^ It has been suggested that the opening chords of Beethoven's Sonata Opus 78 communicate feelings for a young lady then in Beethoven's life, possibly Josephine von Brunswick. (In Heinrich Schenker's remarks in his edition of Beethoven's Sonatas, vol. 2, Dover Publications.)
^ Abert 2007, 624–25.
^ Solomon 1998, 78–79.
^ Hamilton 2008, 101–38.
^ Crutchfield 1983, 7
^ Crutchfield 1983, 5–13
^ Adorno 1997, 99.
^ Adorno 1997, 116.
^ Adorno 1981,, and Adorno 1973,, respectively.
^ Tonality facilitates improvisation, yet it is increasingly difficult for improvisation to encompass radical forms of sound-production or instrumentation. Even atonal improvisation is a conservative exercise. While discussing the Art of The Fugue with Bruno Monsaingeon, Gould describes the later Bach not in basic aesthetic terms, but as an endlessly expanding universe of shades of gray, or colorless contrapuntal texture. Gould was quoting Albert Schweitzer on the first fugue, but felt this description apt for the final fugue. In a 1959 filmed interview, either in Glenn Gould: Off the Record or Glenn Gould: On the Record, Gould had also lamented the end of the common practice period. He illustrated his opinion with a thought experiment, arguing that a child raised with only atonal music would eventually show an original interest in tonality. Koenig & Kroitor 1959a or 1959b.
^ Szwed 2000, 43.
^ Winkler 1978, 16–18.
^ Griffiths 2001.
^ Von Gunden 1983, 32.
^ David Dolan, Piano
^ William Goldstein Composer
^ Eric Barnhill on the Web - Music into Movement into Mind
^ Xlovers on the Web - 100% improvisation concerts
^ 42wina2 on the Web - 100% improvisation concerts
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