In music theory, the key of a piece is a group of pitches, or scale upon which a music composition is created in classical, Western art, and Western pop music. The group features a tonic note and its corresponding chords, also called a tonic or tonic chord, providing a subjective sense of arrival and rest and also has a unique relationship to the other pitches of the same group, their corresponding chords, and pitches and chords outside the group. 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, although major is assumed in a phrase like "this piece is in C." Popular songs are usually in a key, and so is classical music during the common practice period, circa 1650–1900. Longer pieces in the classical repertoire may have sections in contrasting keys.
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 may be said to be "in a key," an unrelated usage referring to the pitches considered "natural" for that instrument. For example, modern trumpets are usually in the key of B♭, since the notes produced without the use of valves correspond to the harmonic series whose fundamental pitch is B♭. (Such instruments are said to be transposing when their written notes differ from concert pitch.)
Keys and tonality
The key usually identifies the tonic note and/or chord: the note and/or major or minor triad that represents the final point of rest for a piece, or the focal point of a section. Although the key of a piece may be named in the title (e.g., Symphony in C), or inferred from the key signature, the establishment of key is brought about via functional harmony, a sequence of chords leading to one or more cadences, 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 the Dorian mode, or Phrygian, etc., and is thus usually thought of as in a specific mode rather than a key. Languages other than English may use other key naming systems.
The notes and chords used within a key are generally drawn from the major or minor scale associated with the tonic triad, but may also include borrowed chords, altered chords, secondary dominants, and the like. All of these notes and chords, however, are used in conventional patterns that serve to establish the primacy of the tonic note and triad.
Cadences are particularly important in the establishment of key. Even cadences that do not include the tonic note or triad, such as half cadences and deceptive cadences, serve to establish key because those chord sequences imply a unique diatonic context.
Short pieces may stay in a single key throughout. A typical pattern for a simple song might be as follows: a phrase 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, then modulate 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 a ritornello, in each key once it was established. In Classical sonata form, the second key was typically marked with a contrasting theme. Another key may be treated as a temporary tonic, called tonicization.
In common 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 some Romantic-era music) the key is deliberately left ambiguous at first. Some arrangements of popular songs, however, shift up a half-step or a whole step sometime during the song (often in a repeat of the final chorus) and thus end in a different key. This is an example of modulation.
It should be noted that the key of the piece ... contributes an indefinable something to the evocative quality. This is very difficult to put into concrete terms, but slow movements in A-flat major do have something in common, as do fast movements in C minor, concerto allegros in D major, etc. There has been disagreement on this point. It has been argued, since standards of pitch level have changed over the centuries, that today we actually hear pieces written two centuries ago in a different (usually higher) key than that intended by the composer. It has been argued that the performer's concept of particular key is actually created by factors such as the 'feel' of the key or tonal center on the keyboard or its appearance in notation. Many musicians, however, tend toward an empirical acceptance of specific moods associated with specific keys, regardless of changes in pitch standards and other factors.
In rock and popular music some pieces, "tend to float back and forth between two keys", with examples including Fleetwood Mac's "Dreams" and The 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 the root of the initiating harmony and persistent use of another note as pitch of melodic resolution and root of the final harmony of each phrase)."
Instruments in a key
Certain musical instruments are sometimes said to 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. The most common kind of clarinet, for example, is said to play in the key of B-flat. This means that a scale written in C major in sheet music actually sounds as a B-flat 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 may be said to be built in a certain key. For example, a brass instrument built in B-flat plays a fundamental note of B-flat, and can play notes in the harmonic series starting on B-flat 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-flat major, although the music is written in D major with implied accidentals.
In Western musical composition, the key of a song has important ramifications for its composition:
- As noted earlier, certain instruments are said to be designed for a certain key, as playing in that key can be physically easier or harder. Thus the choice of key can be an important one when composing for an orchestra, as one must take these elements into consideration.
- In the life of the professional clarinettist, for example, it is common to carry two instruments tuned a semitone apart (B-flat and A) to cope with the needs of composers: Mozart's well-known clarinet concerto is in A Major. To play it on a B-flat instrument is difficult, and to rewrite all the orchestral parts to B-flat major would be an enormous effort. Even so, it is not unheard of for a piece published in B-flat to include notes a semitone (or more) below the range of the common B-flat clarinet. The piece must then be played on a more exotic instrument, or transposed by hand (or at sight) for the slightly larger 'A' clarinet. There are clarinets with an extended range, with a longer bore and additional keys.
- Besides this though, the timbre of almost any instrument is not exactly the same for all notes played on that instrument. For this reason a song that might be in the key of C might sound or "feel" somewhat different (besides being in a different pitch) to an observer if it is transposed to the key of A.
- In addition, since many composers often utilized the piano while composing, the key chosen can possibly have an effect over the composing. This is because the physical fingering is different for each key, which may lend itself to choosing to play and thus eventually write certain notes or chord progressions compared to others, or this may be done on purpose to make the fingering more efficient if the final piece is intended for piano.
- In music that does not use equal temperament, chords played in different keys are qualitatively different.
Key coloration is the difference between the intervals of different keys in a single non-equal tempered tuning, and the overall sound and "feel" the key created by the tuning of its intervals.
Historical irregular musical temperaments usually have the narrowest fifths between the diatonic notes ("naturals") producing purer thirds, and wider fifths among the chromatic notes ("sharps and flats"). Each key then has a slightly different intonation, 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 a wolf fifth, the key on the lowest note of the fifth sounds dramatically different from other keys (and is often avoided). In Pythagorean 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: 4.125, 5, 6) due to E♯+++ (521.44 cents) being a Pythagorean comma (23.46 cents) larger sharp compared to F♮.
Modern music lacks key coloration because it uses equal temperament in which all keys have the same pattern of intonation, differing only in pitch.
- Willi Apel, Harvard Dictionary of Music (Cambridge: Harvard University Press, 1969), 450.
- White, John D. (1976) The Analysis of Music, p. 94. ISBN 0-13-033233-X.
- Ken Stephenson, What to Listen for in Rock: A Stylistic Analysis (New Haven: Yale University Press, 2002), 48. ISBN 978-0-300-09239-4.
- Kent Wheeler Kennan, The Technique of Orchestration, second edition (Englewood Cliffs, New Jersey: Prentice-Hall, Inc., 1970), 1952; ISBN 0-13-900316-9.
- Innig, Renate (1970). System der Funktionsbezeichnung in den Harmonielehren seit Hugo Riemann. Düsseldorf: Gesellschaft zur Förderung der systematischen Musikwissenschaft.
- Rahn, John (1980). Basic Atonal Theory. New York: Longman; London and Toronto: Prentice Hall International. ISBN 0-02-873160-3. Reprinted 1987, New York: Schirmer Books; London: Collier Macmillan.
- Steblin, Rita (1983). A History of Key Characteristics in the 18th and Early 19th Centuries. UMI Research Press, Ann Arbor.
- Christian Schubart's "Affective Key Characteristic"
- Characteristics of Musical Keys - from various sources.
- Key coloration
|Diatonic scales and keys|
|The table indicates the number of sharps or flats in each scale. Minor scales are written in lower case.|