Progressive rock (also referred to as prog rock or prog) is a subgenre of rock music that developed in the late 1960s and early 1970s as part of a "mostly British attempt to elevate rock music to new levels of artistic credibility."
Progressive rock bands pushed "rock's technical and compositional boundaries" by going beyond the standard rock or popular verse-chorus-based song structures. The Oxford Companion to Music states that progressive rock bands "...explored extended musical structures which involved intricate instrumental patterns and textures and often esoteric subject matter." Additionally, the arrangements often incorporated elements drawn from classical, jazz, and world music. Instrumentals were common, while songs with lyrics were sometimes conceptual, abstract, or based in fantasy. Progressive rock bands sometimes used "concept albums that made unified statements, usually telling an epic story or tackling a grand overarching theme." Progressive rock developed from late 1960s psychedelic rock, as part of a wide-ranging tendency in rock music of this era to draw inspiration from ever more diverse influences. The term was initially applied to the music of bands such as King Crimson, Yes, Genesis, Jethro Tull, Pink Floyd, Soft Machine, and Emerson, Lake & Palmer, and reached its peak of popularity in the mid 1970s.
Musical characteristics:
Form: Progressive rock music either avoids common popular music song structures of verse-chorus-bridge, or blurs the formal distinctions by extending sections or inserting musical interludes, often with exaggerated dynamics to heighten contrast between sections. Classical forms are often inserted or substituted, sometimes yielding entire suites, building on the traditional medleys of earlier rock bands. Progressive rock music also often has extended instrumental passages, marrying the classical solo tradition with the improvisational traditions of jazz and psychedelic rock. All of these tend to add length to progressive rock music pieces, which may last longer than twenty minutes and are usually not "songs" per se, but musical works that have a lot more in common with more established musical concepts.
Timbre: (instrumentation and tone color): Early progressive rock groups expanded the timbral palette of traditional rock instrumentation of guitar, organ, bass, and drums by adding instruments more typical of jazz or folk music, such as flute, saxophone, and violin, and more often than not used electronic keyboards, synthesizers, and electronic effects units. Some instruments – most notably the Moog synthesizer, the Mellotron and the Hammond organ – have become closely associated with the genre.
Rhythm: Drawing on their classical, jazz, folk and experimental influences, progressive rock artists are more likely to explore time signatures other than 4/4 and tempo changes. Progressive rock generally tends to be freer in its rhythmic approach than other forms of rock music. The approach taken varies across different works but may range from regular beats, such as 4/4, to unusual compound time signatures, such as 9/8.
Melody and harmony: In progressive rock, the blues inflections of mainstream rock are often supplanted by jazz and classical influences. Melodies are more likely to be modal than based on the pentatonic scale, and are more likely to comprise longer, developing passages than short, catchy ones. Chords and chord progressions may be augmented with 6th, 7th, 9th, and compound intervals; and the I-IV-V is much less common. Allusions to, or even direct quotes from, well-known classical themes are common. Some bands (notably King Crimson) have used atonal or dissonant harmonies, and a few, such as Henry Cow, Shub-Niggurath, and 5uu's, have even worked with rudimentary serialism.
Texture and imagery: Ambient soundscapes and theatrical elements may be used to describe scenes, events or other aspects of the concept. For example, leitmotif is used to represent the various characters in Genesis' "Harold the Barrel" (from Nursery Cryme) and "Robbery, Assault and Battery" (from A Trick of the Tail), and more literally, the sounds of clocks and cash registers are used to represent time and money in Pink Floyd's The Dark Side of the Moon.
Other characteristics:
Technology: To aid timbral exploration, progressive rock bands were often early adopters of new electronic musical instruments and technologies. The analog synthesizer is the instrument best associated with progressive rock – for example, the modular Moog used by ELP, the Minimoog by Yes, the ARP Pro Soloist by Genesis, and the Oberheim by Styx. The mellotron, particularly, was a signature sound of early progressive bands. Pink Floyd utilized an EMS Synthi A synthesizer equipped with a sequencer on their track "On the Run" from their 1973 album The Dark Side of the Moon. In the late 1970s, Robert Fripp, of King Crimson, and Brian Eno developed an analog tape loops effect (Frippertronics). In the 1980s, Frank Zappa used the Synclavier for composing and recording, and King Crimson utilized MIDI-enabled guitars, a Chapman Stick, and electronic percussion.
Concept albums: Collections of songs unified by an elaborate, overarching theme or story are common to progressive rock. As songs by progressive rock acts tend to be quite long, such collections have frequently exceeded the maximum length of recorded media, resulting in packages that require multiple vinyl discs, cassettes, or compact discs in order to present a single album. Concepts have included the historical, fantastical and metaphysical, and even, in the case of Jethro Tull's Thick as a Brick, poked fun at concept albums. One very well-known example is Genesis's The Lamb Lies Down On Broadway, an album about a boy named Rael who undergoes different adventures in search of his brother John.
Lyrical themes: Progressive rock typically has lyrical ambition similar to its musical ambition, tending to avoid typical rock/pop subjects such as love, dancing, etc., rather inclining towards the kinds of themes found in classical literature, fantasy, folklore, social commentary or all of these. Peter Gabriel (Genesis) often wrote surreal stories to base his lyrics around, sometimes including theatrical elements with several characters, while Roger Waters (Pink Floyd) combined social criticism with personal struggles with greed, madness, and death.
Presentation: Album art and packaging is often an important part of the artistic concept. This trend can be seen to have begun with The Beatles' Sgt. Pepper's Lonely Hearts Club Band and played a major part in the marketing of progressive rock. Some bands became as well known for the art direction of their albums as for their sound, with the "look" integrated into the band's overall musical identity. This led to fame for particular artists and design studios, most notably Roger Dean for his work with Yes, and Hipgnosis for their work with Pink Floyd and several other progressive rock groups.
Stage theatrics: Beginning in the early 1970s, some progressive rock bands began incorporating elaborate and sometimes flamboyant stage theatrics into their concerts. Genesis lead singer Peter Gabriel wore many different colourful and exotic costumes within each show and frequently acted out the lyrical narrative of the songs, Pink Floyd would utilize burning gongs and crashing airplanes and inflatables, Yes incorporated futuristic stage sets designed by Roger Dean, performing 'in-the-round', and one of ELP's many stage antics include Emerson's "flying piano" at the California Jam concert, in which a Steinway grand piano would be spun from a hoist.
Source: http://en.wikipedia.org/wiki/Progressive_rock#Characteristics
