Key (music)
In music theory, the key of a piece is the group of pitches, or scale, that forms the basis of a musical composition in Western classical music, art music, and pop music.
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A particular key features a tonic note and its corresponding chords, also called a tonic or tonic chord, which provides a subjective sense of arrival and rest, and also has a unique relationship to the other pitches of the same key, their corresponding chords, and pitches and chords outside the key.[2] Notes and chords other than the tonic in a piece create varying degrees of tension, resolved when the tonic note or chord returns.
The key may be in the major or minor mode, though musicians assume major when this is not specified; for example "This piece is in C" implies that the key of the piece is C major. Popular songs and classical music from the common practice period are usually in one key. Longer pieces in the classical repertoire may have sections in contrasting keys. Key changes within a section or movement are known as modulation.
Overview[edit]
Methods that establish the key for a particular piece can be complicated to explain and vary over music history. However, the chords most often used in a piece in a particular key are those that contain the notes in the corresponding scale, and conventional progressions of these chords, particularly cadences, orient the listener around the tonic.
The key signature is not always a reliable guide to the key of a written piece. It does not discriminate between a major key and its relative minor; the piece may modulate to a different key; if the modulation is brief, it may not involve a change of key signature, being indicated instead with accidentals. Occasionally, a piece in a mode such as Mixolydian or Dorian is written with a major or minor key signature appropriate to the tonic, and accidentals throughout the piece.
Pieces in modes not corresponding to major or minor keys may sometimes be referred to as being in the key of the tonic. A piece using some other type of harmony, resolving e.g. to A, might be described as "in A" to indicate that A is the tonal center of the piece.
An instrument "in a key", is an unrelated usage that means the pitches considered "natural" for that instrument. For example, modern trumpets are usually in the key of B♭, since the notes produced without using the valves correspond to the harmonic series whose fundamental pitch is B♭. (Such instruments are called transposing when their written notes differ from concert pitch.)
A key relationship is the relationship between keys, measured by common tone and nearness on the circle of fifths. See closely related key.
Certain musical instruments play in a certain key, or have their music written in a certain key. Instruments that do not play in the key of C are known as transposing instruments.[5] The most common kind of clarinet, for example, is said to play in the key of B♭. This means that a scale written in C major in sheet music actually sounds as a B♭ major scale when played on the B-flat clarinet—that is, notes sound a whole tone lower than written. Likewise, the horn, normally in the key of F, sounds notes a perfect fifth lower than written.
Similarly, some instruments are "built" in a certain key. For example, a brass instrument built in B♭ plays a fundamental note of B♭, and can play notes in the harmonic series starting on B♭ without using valves, fingerholes, or slides to alter the length of the vibrating column of air. An instrument built in a certain key often, but not always, uses music written in the same key (see trombone for an exception). However, some instruments, such as the diatonic harmonica and the harp, are in fact designed to play in only one key at a time: accidentals are difficult or impossible to play.
The highland bagpipes are built in B♭ major, though the music is written in D major with implied accidentals.
In Western musical composition, the key of a piece has important ramifications for its composition: