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 a tonic (main) note and its corresponding chords, also called a tonic or tonic 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 the major mode, minor mode, or one of several other modes. 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 a single key; longer pieces in the classical repertoire may have sections in contrasting keys. Key changes within a section or movement are known as modulation.
Background
Music is made from audible vibrations, such as from oscillating strings or air moving through reeds.[3]. Humans generally perceive some vibrations as sounding "higher" or "lower" than others, creating a subjective perception called pitch.[4] As a medium vibrates faster, its higher frequency is perceived as higher pitch.[5] In Western tonal music, specific frequencies are grouped into twelve pitch classes. Seven of these are considered "natural" pitches, and are represented by the letters A, B, C, D, E, F, and G.[6][7]
Humans perceive frequencies logarithmically, not linearly. The ratio between two frequencies determines how different they sound.[8] If one vibration has twice the frequency of another, they sound similar enough to be considered the same pitch class; they are said to be one octave apart.[9][10][11] Pitches separated by an octave are sometimes given numbers to reduce ambiguity. For example, the lowest C playable on a standard piano is designated C1, while the pitch with twice the frequency (one octave higher) is C2.[11][a]
On a piano, the seven natural pitches are played with white keys. The black keys play intermediate pitches which are notated with the symbols ♯ and ♭. The musical distance between adjacent keys is one semitone. A Major Scale begins and ends on a starting pitch, called the Tonic, and follows a pattern of semitone and whole tone steps. In this diagram, the dots represent the seven pitches of the Major scale starting from A, the basis for the key of A Major.
On a piano, each white key represents one of the seven "natural" pitches. These are arranged from A to G, followed by another A one octave higher. Among these pitches, the relative increases in frequency from B to C and from E to F are smaller than the changes between other adjacent pitches. This smaller distance is called a semitone, while the larger distance from e.g. A to B is a whole tone. When two natural pitches are a whole tone apart, a black key represents an intermediate pitch. Instead of using separate letters, these pitches are denoted with the accidentals♯ (sharp) and ♭ (flat), which represent raising or lowering a natural pitch by one semitone. The pitch between G and A may be denoted as either G♯ (G plus one semitone) or A♭ (A minus one semitone). In musical terminology, G♯ and A♭ are considered enharmonic.[13]
Most Western music is built around major and minor scales. These scales use seven of the twelve pitches, arranged in ascending or descending order, and beginning and ending with the same pitch one octave apart.[14][15][7] An ascending major scale moves between pitches with the pattern tone, tone, semitone, tone, tone, tone, semitone.[16][17][b] An ascending minor scale instead uses the pattern tone, semitone, tone, tone, semitone, tone, tone; this results in the third, sixth, and seventh pitches being one semitone lower compared to the major scale.[19]. On a piano, a major scale beginning from C and a minor scale beginning from A each contain only natural pitches and use exclusively white keys; the two scales are considered distinct "modes" of the same group of pitches.[20][21] In contrast, a major scale beginning from A uses the pitches A, B, C♯, D, E, F♯, G♯, A.[22][c] The pitch which begins and ends a given scale is called its tonic.[25]
Definition
A key is a way to classify a piece of music. It represents that the piece is oriented around a specific Major or Minor scale.[26] The name of a key, such as A Major, contains both a Tonic pitch and a Mode (either Major or Minor). Because there are 12 pitches to use as a tonic, there are 24 distinct keys.[20][27][d] If the mode is not specified, the simplified term "key of C" usually implies the key is C Major.[28]
If a piece of music is in a key, it mostly uses pitches from the corresponding scale.[20] The seven pitches that belong to the scale are called diatonic pitches, while the remaining five are called chromatic pitches.[15] A key does not prohibit the use of chromatic pitches, but they will be rarer than diatonic pitches.[26] The key's tonic represents a pitch of "stability" for the music to orient around. In particular, a composition almost always ends on the tonic.[20][29]
Not all music has a well defined key. Some classical compositions, such as Chopin's Prelude op. 28 no. 2 and Wagner's Tristan und Isolde, do not clearly follow these patterns.[30] Modern atonal music, including the works of Arnold Schoenberg, has no tonal stability and freely interweaves all twelve pitches.[31][32]
Notation
(Top) The A Major scale contains three pitches with accidentals: C♯, F♯, and G♯.
(Bottom) This can be simplified using a key signature with three initial ♯ symbols. Unless otherwise noted, these will apply to every instance of the pitches C, F, and G.
Music is written using a staff (music) with five or more parallel lines. Pitches are represented by notes placed either on a line or in the space between lines. The relationship between pitch and position is defined by a symbol called a clef. In a standard staff with a treble clef, the bottom line represents the pitch E, the line above represents G, and the space between the two lines is F. The pitch between F and G cannot be represented solely by position, so it is represented by marking either an F or G note with an accidental (♯ or ♭).[33]
In the keys of C Major and A Minor, the common diatonic pitches do not use accidentals.[34] When writing in other keys, the positions themselves can be marked with accidentals as a shorthand. For example, a ♯ accidental on a line or space representing F means that, unless otherwise specified, all F pitches should be raised one semitone.[21][34][11]. Another accidental, ♮ (natural), overrides this general rule and represents the natural pitch.[35][36] When writing this shorthand notation, known as a key signature, Sharps are always arranged in the order F, C, G, D, A, E, B, while Flats use the opposite order.[34]
A key signature allows the corresponding major or minor scale to be written without accidentals.[37][28] Any remaining accidentals represent chromatic pitches which are less closely associated with the key.[38] However, a key signature does not uniquely specify a key, since it does not identify the tonic. Any key signature could represent either a major or minor key with the same pitches but different tonics.[20][39]
Modulation
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, modulate 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.
In rock and popular music some pieces change back and forth, or modulate, between two keys. Examples of this include 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)."[40]
Instruments in a 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.[41] 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:
As noted earlier, certain instruments are 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 clarinetist, for example, it is common to carry two instruments tuned a semitone apart (B♭ 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♭ instrument is difficult, and to rewrite all the orchestral parts to B♭ major would be an enormous effort. Even so, it is not unheard of for a piece published in B♭ to include notes a semitone (or more) below the range of the common B♭ 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 piece that might be in the key of C might sound or "feel" somewhat different (besides being in a different pitch) to a listener 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.
References
↑ Berlin, Boris; Sclater, Molly; and Sinclair, Kathryn (2006). Keys to Music Rudiments, p.21. Gordon V. Thompson. ISBN9781457496509. "The key signature, meaning 'a sign which shows the key'..."
↑ Historically, the exact relationship between frequency and pitch varied across different places and times. Today, international standard concert pitch defines the pitch A4 as the frequency 440 Hertz. Other pitches can be mathematically derived from this baseline.[12][5]
↑ The major pentatonic scale is a subset of the major scale. It excludes the fourth and seventh pitches, so that all five remaining pitches are at least a whole tone apart[18]
↑ Scales are written using each letter from A through G, and without intermixing ♯ and ♭ accidentals. The pitch between C and D could be written D♭ instead of C♯, but it would be incorrect to write this scale as A, B, D♭, D, E, F♯, G♯, A.[23][24]
↑ Although there are only 24 possible keys, there are more than 24 possible key names. For example, C♯ Major and D♭ Major are equivalent names for the same key. [20]
Works Cited
Blatter, Alfred (2007). Revisiting Music Theory: A Guide To The Practice. New York: Routledge. ISBN0-415-97440-2.
de Clercq, Trevor (2025). The Practice Of Popular Music: Understanding Harmony, Rhythm, Melody, And Form In Commercial Music. New York: Routledge. ISBN978-1-032-36290-8.
Kennedy, Michael; Kennedy, Joyce Bourne; Rutherford-Johnson, Tim (2013). The Oxford dictionary of music (Sixthed.). Oxford: Oxford University Press. ISBN978-0-19-957854-2.
Laitz, Steven G. (2016). The Complete Musician: An Integrated Approach To Theory, Analysis And Listening (Fourthed.). Oxford; New York: Oxford University Press. ISBN978-0-19-934709-4.
Randel, Don Michael, ed. (2003). The Harvard Dictionary of Music (4thed.). Cambridge, Mass: Belknap Press of Harvard University Press. ISBN0-674-01163-5.
Roederer, Juan (2008). The Physics and Psychophysics of Music (Fourthed.). Springer. ISBN978-0-387-09474-8.
Roig-Francolí, Miguel A. (2021). Understanding Post-Tonal Music (Seconded.). New York; London: Routledge, Taylor & Francis Group. ISBN978-0-367-35537-1.
Further reading
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. ISBN0-02-873160-3. 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.
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