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Inmusic theory, thekey of a piece is the group of pitches, orscale, that forms the basis of amusical composition in Westernclassical music,jazz music,art music, andpop music.
Tonality (from "Tonic") or key: Music which uses the notes of a particular scale is said to be "in the key of" that scale or in the tonality of that scale.[1]
A particular key features atonic (main)note and its correspondingchords, also called atonic ortonic chord, which provides a subjective sense of arrival and rest. The tonic 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 themajor 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 thecommon practice period are usually in one key. Longer pieces in the classical repertoire may have sections incontrasting keys. Key changes within a section or movement are known asmodulation.
Methods that establish the key for a particular piece can be complicated to explain and vary over music history.[citation needed] However, the chords most often used in a piece in a particular key are those that contain the notes in the correspondingscale, and conventionalprogressions of these chords, particularlycadences, orient the listener around the tonic.
Thekey signature is not always a reliable guide to the key of a written piece. It does not discriminate between a major key and itsrelative minor; the piece maymodulate to a different key; if the modulation is brief, it may not involve a change of key signature, being indicated instead withaccidentals. Occasionally, a piece in amode such asMixolydian orDorian 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 ofharmony, resolving e.g. to A, might be described as "in A" to indicate that A is thetonal center of the piece.
An instrument "in a key", is an unrelated usage that means the pitches considered "natural" for that instrument. For example, moderntrumpets are usually in the key of B♭, since the notes produced without using the valves correspond to theharmonic series whose fundamental pitch is B♭. (Such instruments are calledtransposing when their written notes differ fromconcert pitch.)
Akey relationship is the relationship between keys, measured bycommon tone and nearness on thecircle of fifths. Seeclosely related key.
The key usually identifies thetonic note and/or chord: the note and/ormajor orminortriad that represents the final point of rest for a piece, or the focal point of a section. Though the key of a piece may be named in the title (e.g., Symphony in C major), or inferred from thekey signature, the establishment of key is brought about viafunctional harmony, a sequence of chords leading to one or morecadences, and/or melodic motion (such as movement from the leading-tone to the tonic). For example, the key of G includes the following pitches: G, A, B, C, D, E, and F♯; and its corresponding tonic chord is G—B—D. Most often at the beginning and end of traditional pieces during the common practice period, the tonic, sometimes with its corresponding tonic chord, begins and ends a piece in a designated key. A key may be major or minor. Music can be described as being in theDorian mode, orPhrygian, etc., and is thus usually thought of as in a specificmode rather than a key. Languages other than English may use otherkey naming systems.
People sometimes confuse key withscale. Ascale is an ordered set of notes typically used in a key, while thekey is the "center of gravity" established by particularchord progressions.[3]
Cadences are particularly important in the establishment of key. Even cadences that do not include the tonic note or triad, such ashalf cadences anddeceptive cadences, serve to establish key because those chord sequences imply a uniquediatonic context.
Short pieces may stay in a single key throughout. A typical pattern for a simplesong might be as follows: aphrase ends with a cadence on the tonic, a second phrase ends with a half cadence, then a final, longer, phrase ends with an authentic cadence on the tonic.
More elaborate pieces may establish the main key, thenmodulate to another key, or a series of keys, then back to the original key. In the Baroque it was common to repeat an entire phrase of music, called aritornello, in each key once it was established. In Classicalsonata form, the second key was typically marked with a contrastingtheme. Another key may be treated as a temporary tonic, calledtonicization.
Incommon practice period compositions, and most of the Western popular music of the 20th century, pieces always begin and end in the same key, even if (as in someRomantic-era music) the key is deliberately left ambiguous at first. Somearrangements of popular songs, however, modulate sometime during the song (often in a repeat of the finalchorus) and thus end in a different key. This is an example ofmodulation.
Inrock andpopular music some pieces change back and forth, or modulate, between two keys. Examples of this includeFleetwood Mac's "Dreams" andThe Rolling Stones' "Under My Thumb". "This phenomenon occurs when a feature that allows multiple interpretations of key (usually a diatonic set as pitch source) is accompanied by other, more precise evidence in support of each possible interpretation (such as the use of one note as theroot of the initiating harmony and persistent use of another note as pitch of melodic resolution and root of the final harmony of each phrase)."[4]
Certainmusical 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 astransposing instruments.[5] The most common kind ofclarinet, for example, is said to play in the key of B♭. This means that a scale written in C major insheet music actually sounds as a B♭ major scale when played on the B-flat clarinet—that is, notes sound awhole tone lower than written. Likewise, thehorn, normally in the key of F, sounds notes aperfect fifth lower than written.
Similarly, some instruments are "built" in a certain key. For example, abrass instrument built in B♭ plays afundamental note of B♭, and can play notes in theharmonic 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 (seetrombone for an exception). However, some instruments, such as the diatonicharmonica and theharp, 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:
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Key coloration is the difference between theintervals of different keys in a single non-equal tempered tuning, and the overall sound and "feel" of the key created by the tuning of its intervals.
Historical irregularmusical temperaments usually have the narrowestfifths between thediatonic notes ("naturals") producing purerthirds, and wider fifths among the chromatic notes ("sharps and flats"). Each key then has a slightly differentintonation, hence different keys have distinct characters. Such "key coloration" was an essential part of much eighteenth- and nineteenth-century music and was described in treatises of the period.
For example, in tunings with awolf fifth, the key on the lowest note of the fifth sounds dramatically different from other keys (and is often avoided). InPythagorean tuning on C (C, E+, G: 4, 5, 6), the major triad on C is just while the major triad on E♯+++ (F♮) is noticeably out of tune (E♯+++, A+, C:4+1⁄8, 5, 6) due to E♯+++ (521.44 cents) being aPythagorean comma (23.46 cents) larger sharp compared to F♮.
Music usingequal temperament lacks key coloration because all keys have the same pattern of intonation, differing only in pitch.
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