Electric guitars can have solid, semi-hollow, or hollow bodies, and produce little sound without amplification. Electromagnetic pickups convert the vibration of the steel strings into electrical signals which are fed to an amplifier through a cable or radio transmitter. The sound is frequently modified by other electronic devices or the natural distortion of valves (vacuum tubes) in the amplifier. There are two main types of pickup, single and double coil (or humbucker), each of which can be passive or active. The electric guitar is used extensively in jazz, blues, and rock and roll, and was commercialized by Gibson in collaboration with Les Paul, and independently by Leo Fender of Fender Music. The lower fretboard action (the height of the strings from the fingerboard) and its electrical amplification lend the electric guitar to some techniques which are less frequently used on acoustic guitars. These include tapping, extensive use of legato through pull-offs and hammer-ons (also known as slurs), pinch harmonics, volume swells, and use of a tremolo arm or effects pedals.

Seven-strings were popularized in the 1980s and 1990s in part due to the release of the Ibanez Universe guitar, endorsed by Steve Vai. Other artists go a step further, by using an 8 string guitar with two extra low strings. Although the most common 7-string has a low B string, Roger McGuinn (of The Byrds and Rickenbacker) uses an octave G string paired with the regular G string as on a 12 string guitar, allowing him to incorporate chiming 12 string elements in standard 6 string playing.

The electric bass guitar is similar in tuning to the traditional double bass viol. Hybrids of acoustic and electric guitars are also common. There are also more exotic varieties, such as guitars with two, three,[12] or rarely four necks, all manner of alternate string arrangements, fretless fingerboards (used almost exclusively on bass guitars, meant to emulate the sound of a stand-up bass), 5.1 surround guitar, and such.

Some electric guitar and electric bass guitar models feature Piezoelectric pickups, which function as transducers to provide a sound closer to that of an acoustic guitar with the flip of a switch or knob, rather than switching guitars.

Before the development of the electric guitar and the use of synthetic materials, a guitar was defined as being an instrument having "a long, fretted neck, flat wooden soundboard, ribs, and a flat back, most often with incurved sides".[1] Instruments similar to the guitar have been popular for at least 5,000 years. The six string classical guitar first appeared in Spain but was itself the product of a long and complex history of diverse influences. Like virtually all other stringed European instruments, the guitar ultimately traces back thousands of years, via the Middle East, to a common ancient origin from instruments then known in central Asia and India. It is therefore very distantly related with contemporary instruments such as the Iranian tanbur and setar and the Indian sitar. The oldest known iconographic representation of an instrument displaying all the essential features of a guitar being played is a 3300 year old stone carving of a Hittite bard.[2] The modern word, guitar, was adopted into English from Spanish guitarra, derived from the Latin word cithara, which in turn was derived from the earlier Greek word kithara,[3] which perhaps derives from Persian sihtar.[4] Sihtar itself is related to the Indian instrument, the sitar.
Illustration from a Carolingian Psalter from the 9th century, showing a guitar-like plucked instrument.
Illustration from a Carolingian Psalter from the 9th century, showing a guitar-like plucked instrument.

The modern guitar is descended from the Roman cithara brought by the Romans to Hispania around 40 AD, and further adapted and developed with the arrival of the four-string oud, brought by the Moors after their conquest of the Iberian peninsula in the 8th century.[5] Elsewhere in Europe, the indigenous six-string Scandinavian lut (lute), had gained in popularity in areas of Viking incursions across the continent. Often depicted in carvings c. 800 AD, the Norse hero Gunther (also known as Gunnar), played a lute with his toes as he lay dying in a snake-pit, in the legend of Siegfried.[6] By 1200 AD, the four string "guitar" had evolved into two types: the guitarra morisca (Moorish guitar) which had a rounded back, wide fingerboard and several soundholes, and the guitarra latina (Latin guitar) which resembled the modern guitar with one soundhole and a narrower neck.[7]

The Spanish vihuela or "viola da mano", a guitar-like instrument of the 15th and 16th centuries is, due to its many similarities, usually considered the immediate ancestor of the modern guitar. It had lute-style tuning and a guitar-like body. Its construction had as much in common with the modern guitar as with its contemporary four-course renaissance guitar. The vihuela enjoyed only a short period of popularity as it was superseded by the guitar; the last surviving publication of music for the instrument appeared in 1576. It is not clear whether it represented a transitional form or was simply a design that combined features of the Arabic oud and the European lute. In favor of the latter view, the reshaping of the vihuela into a guitar-like form can be seen as a strategy of differentiating the European lute visually from the Moorish oud.

The Vinaccia family of luthiers is known for developing the mandolin, and may have built the oldest surviving six string guitar. Gaetano Vinaccia (1759 – after 1831)[8] has his signature on the label of a guitar built in Naples, Italy for six strings with the date of 1779.[9][10] This guitar has been examined and does not show tell-tale signs of modifications from a double-course guitar although fakes are known to exist of guitars and identifying labels from that period.

Modern dimensions of the classical instrument were established by Antonio Torres Jurado (1817-1892), working in Seville in the 1850s. Torres and Louis Panormo of London (active 1820s-1840s) were both responsible for demonstrating the superiority of fan strutting over transverse table bracing.[11]

The electric guitar was patented by George Beauchamp in 1936. Beauchamp co-founded Rickenbacher which used the horseshoe-magnet pickup. However, it was Danelectro that first produced electric guitars for the wider public.

Greek philosophers and Ancient Indians defined music as tones ordered horizontally as melodies, and vertically as harmonies. Music theory, within this realm, is studied with the presupposition that music is orderly and often pleasant to hear. However, in the 20th century, composers challenged the notion that music had to be pleasant by creating music that explored harsher, darker timbres. The existence of some modern-day music genres such as death metal and grindcore, which enjoy an extensive underground following, indicate that even the harshest sounds can be considered music if the listener is so inclined.

20th century composer John Cage disagreed with the notion that music must consist of pleasant, discernible melodies. Instead, he argued that any sounds we can hear can be music, saying, for example, "There is no noise, only sound,".[2] According to musicologist Jean-Jacques Nattiez, "the border between music and noise is always culturally defined--which implies that, even within a single society, this border does not always pass through the same place; in short, there is rarely a consensus.... By all accounts there is no single and intercultural universal concept defining what music might be, except that it is "sound through time"."[3]

The creation, performance, significance, and even the definition of music vary according to culture and social context. Music ranges from strictly organized compositions (and their recreation in performance), through improvisational music to aleatoric forms. Music can be divided into genres and sub-genres, although the dividing lines and relationships between music genres are often subtle, sometimes open to individual interpretation, and occasionally controversial. Within "the arts", music can be classified as a performing art, a fine art, or an auditory art form.