View source for Key signature

{{short description|Set of musical alterations}}
{{For|use in cryptography|Key signature (cryptography)}}
{{more citations needed|date=May 2025}}
{{Image frame|content=<score>{ \magnifyStaff #2 \omit Score.TimeSignature \key bes \major s^"" }</score>|width=200|caption=Key signature showing B{{Music|b}} and E{{Music|b}} (the key of [[B-flat major|B{{flat}} major]] or [[G minor]])}}
{{Image frame|content=<score>{ \magnifyStaff #2 \omit Score.TimeSignature \key d \major s^"" }</score>|width=200|caption=Key signature showing F{{Music|#}} and C{{Music|#}} (the key of [[D major]] or [[B minor]])}}

In [[Western culture|Western]] [[musical notation]], a '''key signature''' is a set of [[Sharp (music)|sharp]] ({{Music|sharp}}), [[Flat (music)|flat]] ({{Music|b}}), or rarely, [[Natural (music)|natural]] ({{Music|natural}}) symbols placed on the [[staff (music)|staff]] at the beginning of a section of music. The initial key signature in a piece is placed immediately after the [[clef]] at the beginning of the first line. If the piece contains a section in a different [[Key (music)|key]], the new key signature is placed at the beginning of that section.

In a key signature, a sharp or flat symbol on a line or space of the staff indicates that the [[note (music)|note]] represented by that line or space is to be played a [[semitone]] higher (sharp) or lower (flat) than it would otherwise be played. This applies through the rest of the piece or until another key signature appears. Each symbol applies to comparable notes in all [[octave]]s—for example, a flat on the fourth space  of the [[Clef#Treble clef|treble staff]] (as in the diagram) indicates that all notes notated as [[E (musical note)|Es]] are played as [[E♭ (musical note)|E-flats]], including those on the bottom line of the staff.

Most of this article addresses key signatures that represent the [[Diatonic and chromatic|diatonic]] keys of Western music. These contain either flats or sharps, but not both, and the different key signatures add flats or sharps according to the order shown in the [[circle of fifths]].

Each [[Major scale|major]] and [[Minor scale|minor]] [[key (music)|key]] has an associated key signature, showing up to seven flats or seven sharps, that indicates the notes used in its scale. Music was sometimes notated with a key signature that did not match its key in this way—this can be seen in some [[Baroque music|Baroque]] pieces,<ref>Schulenberg, David. ''Music of the Baroque''. New York: Oxford University Press, 2001. [https://books.google.com/books?id=P4x3aKvOQWAC&pg=PA72&vq=%22the+key+of+a+baroque+work%22&source=gbs_search_r&cad=1_1&sig=ACfU3U3x7lhOyyIiT-O_HsTZlZxw8FrkSA p. 72.]. "(…) to determine the key of a Baroque work one must always analyze its tonal structure rather than rely on the key signature."</ref> or transcriptions of traditional [[Mode (music)|modal]] [[Folk music|folk]] tunes.<ref>Cooper, David. ''The Petrie Collection of the Ancient Music of Ireland''. Cork: Cork University Press, 2005. [https://books.google.com/books?id=PzrfncNnr4cC&pg=PA25-IA13&vq=%22In+a+few+cases+Petrie+has+given+what+is+clearly+a+modal+melody+a+key+signature+which+suggests+that+it+is+actally+in+a+minor+key%22&source=gbs_search_r&cad=1_1&sig=ACfU3U0BqVPTuQnnaH32iLpCvrYnyT143Q p. 22]. "In a few cases Petrie has given what is clearly a modal melody a key signature which suggests that it is actually in a minor key. For example, ''Banish Misfortune'' is presented in D minor, although it is clearly in the Dorian mode."</ref>

== Overview ==
{{Image frame|content=<score>{
\omit Score.TimeSignature \relative c' {
  \time 2/1 b cis dis e fis gis ais b} }</score>|width=225|caption=[[B major]] scale using accidentals instead of a key signature}}
{{Image frame|content=<score>{
\omit Score.TimeSignature \relative c' {
  \key b \major \time 2/1 b cis dis e fis gis ais b} }</score>|width=260|caption=B major scale with the usual key signature}}

With any note as a starting point, a certain series of [[Interval (music)|intervals]] produces a [[major scale]]: whole step, whole, half, whole, whole, whole, half.

Starting on C, this yields C-D-E-F-G-A-B-C (a C-major scale). There are no sharps or flats in this scale, so the key signature for C has no sharps or flats in it. Starting on any other note requires that at least one of these notes be changed (raised or lowered) to preserve the major scale pattern. These raised or lowered notes form the key signature. Starting the pattern on D, for example, yields D-E-F{{music|sharp}}-G-A-B-C{{music|sharp}}-D, so the key signature for D major has two sharps—F{{music|sharp}} and C{{music|sharp}}.

Key signatures indicate that this applies to the section of music that follows, showing the reader which key the music is in, and making it unnecessary to apply accidentals to individual notes.

In standard [[Music notation#Modern notation|music notation]], the order in which sharps or flats appear in key signatures is uniform, following the [[circle of fifths]]: F{{music|sharp}}, C{{music|sharp}}, G{{music|sharp}}, D{{music|sharp}}, A{{music|sharp}}, E{{music|sharp}}, B{{music|sharp}}, and B{{music|flat}}, E{{music|flat}}, A{{music|flat}}, D{{music|flat}}, G{{music|flat}}, C{{music|flat}}, F{{music|flat}}. Musicians can identify the key by the number of sharps or flats shown, since they always appear in the same order. A key signature with one sharp must show [[F♯ (musical note)|F-sharp]],<ref name="orderofsharp">{{Cite web |url=https://www.dummies.com/art-center/music/guitar/how-to-read-key-signatures/ |title=How to Read Key Signatures}}</ref> which indicates [[G major]] or [[E minor]].

There can be exceptions to this, especially in 20th-century music, if a piece uses an unorthodox or synthetic scale and an invented key signature to reflect that. This may consist of sharps or flats that are not in the usual order, or of sharps combined with  flats (e.g., F{{music|sharp}} and B{{music|flat}}). Key signatures of this kind can be found in the music of [[Béla Bartók]], for example.

In a score, [[transposing instrument]]s will show a different key signature to reflect their transposition but their music is in the same concert key as the other instruments. Percussion instruments with indeterminate pitch will not show a key signature, and  [[timpani]] parts are sometimes written without a key signature (early timpani parts were sometimes notated with the high drum as "C" and the low drum a fourth lower as "G", with actual pitches indicated at the beginning of the music, e.g., "timpani in D–A"). In [[polytonal]] music, where different parts are actually in different keys sounding together, instruments may be notated in different keys.

[[File:Circle of fifths with musical keyboard.svg|thumb|right|400px|[[Circle of fifths]] showing [[major key|major]] and [[minor key]]s and their signatures]]

== Conventions ==
The order in which sharps or flats appear in key signatures is illustrated in the diagram of the [[circle of fifths]]. Starting the major scale pattern (whole step, whole, half, whole, whole, whole, half) on C requires no sharps or flats. Proceeding clockwise in the diagram starts the scale a fifth higher, on G. Starting on G requires one sharp, F{{music|sharp}}, to form a major scale. Starting another fifth higher, on D, requires F{{music|sharp}} and C{{music|sharp}}. This pattern continues, raising the seventh scale degree of each successive key. As the scales become notated in flats, this is shown by eliminating one of the flats. This is strictly a function of notation—the seventh scale degree is still being raised by a semitone compared to the previous key in the sequence. Going counter-clockwise from C results in lowering the fourth scale degree with each successive key (starting on F requires a B{{music|flat}} to form a major scale). Each major key has a relative minor key that shares the same key signature. The relative minor is always a [[minor third]] lower than its relative major.

The key signatures with seven flats and seven sharps are usually notated in their enharmonic equivalents. [[C-sharp major|C{{music|#}} major]] (seven sharps) is usually written as [[D-flat major|D{{music|b}} major]] (five flats) and [[C-flat major|C{{music|b}} major]] is usually written as [[B major]].

{{Image frame|content=<score>  {
\omit Score.TimeSignature
<< \new ChordNames \chordmode { ais1:m a:m }
\new Staff \relative c' {
  \key ais \minor <ais cis eis ais>1 \bar "||" \key a \minor <a c e a>} >> }
</score>|width=266|align=right|caption=Natural key signature: a key signature with seven [[Natural (music)|naturals]] ({{Music|natural}}) used to cancel the seven sharps ({{Music|sharp}}) of the previous signature.}}

The key signature may be changed at any time in a piece by providing a new signature. If the new signature has no sharps or flats, a signature of naturals, as shown, is used to cancel the preceding signature. If a change in signature occurs at the start of a new line on the page, where a signature would normally appear, the new signature is customarily repeated at the end of the previous line to make the change more conspicuous.

=== Variations ===
{{unreferenced section|date=May 2025}}
When a key signature changes from sharps to flats or vice versa, the old key signature can be cancelled with a matching set of naturals before the new key signature is shown. This was a frequent convention in older notation styles but newer music and newer editions of old music sometimes simply show the new signature without the canceling naturals. These naturals are necessary, however, if the new key signature has no sharps or flats (C major, A minor, or an open key signature).

Similarly, when a flat key changes to fewer flats, or a sharp key changes to fewer sharps, the older convention was to use naturals to cancel the flats or sharps being eliminated before the new signature is written. Modern usage often simply shows the new signature without these naturals. The use of natural signs is still required if the new key signature has no sharps or flats.

When a flat key changes to more flats or a sharp key changes to more sharps, the new signature is simply written in without using naturals to cancel the old signature. This convention applies in both traditional and newer styles.

At one time it was usual to precede the new signature with a [[barline|double barline]] even if it was not otherwise required, but it has become increasingly common to simply use a single barline. The courtesy signature that appears at the end of a line immediately before a change is usually preceded by an additional barline and the line at the very end of the staff is omitted.

If both naturals and a new key signature appear at a key signature change, there are also modern variations about where a barline will be placed. In some scores by Debussy the barline is placed after the naturals but before the new key signature. Hitherto, it would have been usual to place all the symbols after the barline.

The A{{music|sharp}} which is the fifth sharp in the sharp signatures may occasionally be notated on the top line of the bass staff, whereas it is more usually found in the lowest space on that staff. An example of this can be seen in the full score of [[Ottorino Respighi]]'s ''[[Pines of Rome]]'', in the third section, "Pines of the Janiculum" (which is in [[B major]]), in the bass-clef instrumental parts.

In the case of seven-flat key signatures, the final F{{music|flat}} may occasionally be seen on the second-top line of the bass staff, whereas it would more usually appear on the space below the staff. An example of this can be seen in [[Isaac Albéniz]]'s ''[[Iberia (Albéniz)|Iberia]]'': first movement, "Evocación", which is in [[A-flat minor|A{{music|flat}}]] minor.

=== Double flats and sharps ===
Key signatures can extend into [[double flat]]s or [[double sharp]]s, but this is extremely rare. For example, the key of [[G sharp major|G{{music|#}} major]] would have eight sharps, requiring an F double-sharp (F{{music|x}}) and six single sharps. The key of [[A flat major|A{{music|b}} major]], with four flats, is [[Enharmonic equivalence|enharmonically equivalent]] and would generally be used instead. Although the notation of key signatures could theoretically extend beyond single flats or sharps, a key signature with more than one or two double flats or sharps would be exceedingly hard to read and would be replaced by the enharmonically equivalent key signature.
:{| class="wikitable"
![[Major key|Major]]
!Key signature
![[Minor key|Minor]]
|-
|[[F-flat major|F{{Music|flat}} major]] ([[E major]])
|8 flats (4 sharps)
|[[D-flat minor|D{{Music|flat}} minor]] ([[C-sharp minor|C{{Music|sharp}} minor]])
|-
|B{{Music|doubleflat}} major ([[A major]])
|9 flats (3 sharps)
|G{{Music|flat}} minor ([[F-sharp minor|F{{Music|sharp}} minor]])
|-
|E{{Music|doubleflat}} major ([[D major]])
|10 flats (2 sharps)
|C{{Music|flat}} minor ([[B minor]])
|-
|A{{Music|doubleflat}} major ([[G major]])
|11 flats (1 sharp)
|F{{Music|flat}} minor ([[E minor]])
|-
|D{{Music|doubleflat}} major ([[C major]])
|12 flats (no sharps or flats)
|B{{Music|doubleflat}} minor ([[A minor]])
|-
|G{{Music|doubleflat}} major ([[F major]])
|13 flats (1 flat)
|E{{Music|doubleflat}} minor ([[D minor]])
|-
|C{{Music|doubleflat}} major ([[B-flat major|B{{Music|flat}} major]])
|14 flats (2 flats)
|A{{Music|doubleflat}} minor ([[G minor]])
|-
|[[G-sharp major|G{{Music|sharp}} major]] ([[A-flat major|A{{Music|flat}} major]])
|8 sharps (4 flats)
|[[E-sharp minor|E{{Music|sharp}} minor]] ([[F minor]])
|-
|D{{Music|sharp}} major ([[E-flat major|E{{Music|flat}} major]])
|9 sharps (3 flats)
|B-sharp minor|B{{Music|sharp}} minor ([[C minor]])
|-
|A{{Music|sharp}} major ([[B-flat major|B{{Music|flat}} major]])
|10 sharps (2 flats)
|F{{Music|doublesharp}} minor ([[G minor]])
|-
|E{{Music|sharp}} major ([[F major]])
|11 sharps (1 flat)
|C{{Music|doublesharp}} minor ([[D minor]])
|-
|B{{Music|sharp}} major ([[C major]])
|12 sharps (no flats or sharps)
|G{{Music|doublesharp}} minor ([[A minor]])
|-
|F{{Music|doublesharp}} major ([[G major]])
|13 sharps (1 sharp)
|D{{Music|doublesharp}} minor ([[E minor]])
|-
|C{{Music|doublesharp}} major ([[D major]])
|14 sharps (2 sharps)
|A{{Music|doublesharp}} minor ([[B minor]])
|}
A piece in a major key might modulate up a [[Perfect fifth|fifth]] to the [[Dominant (music)|dominant]] (a common occurrence in Western music), resulting in a new key signature with an additional sharp. If the original key was C-sharp, such a [[Modulation (music)|modulation]] would lead to the key of G-sharp major (with eight sharps) requiring an F{{Music|x}} in place of the F{{Music|#}}. This section could be written using the enharmonically equivalent key signature of A-flat major instead. [[Claude Debussy]]'s ''[[Suite bergamasque]]'' does this: in the third movement "Clair de lune" the key shifts from D-flat major to D-flat minor (eight flats) for a few measures but the passage is notated in C-sharp minor (four sharps); the same happens in the final movement, "Passepied", in which a G-sharp major section is written as A-flat major.

Such passages may instead be notated with the use of double-sharp or double-flat accidentals, as in this example from [[Johann Sebastian Bach]]'s ''[[Well-Tempered Clavier]]'', which has this passage in G-sharp major in measures 10-12.

:[[File:G-sharp major example 2.png]]

While these keys are sometimes notated with accidentals as in this example, the use of a key signature containing double flats or sharps is very rare. The final pages of [[John Foulds]]' ''[[A World Requiem]]'' are written in [[G-sharp major|G♯ major]] (with F{{music|x}} in the key signature), No. 18 of [[Anton Reicha]]'s ''Practische Beispiele'' is written in B{{music|#}} major, and the third movement of [[Victor Ewald]]'s [[Brass quintet|Brass Quintet]] Op. 8 is written in [[F♭ major]] (with B{{music|bb}} in the key signature).<ref name=":0">{{IMSLP|work=Practische Beispiele (Reicha, Anton)|cname=Anton Reicha: ''Practische Beispiele'', pp. 52-53.}}</ref><ref>{{cite web |author=<!--Staff writer(s); no by-line.--> |title=Ewald, Victor: Quintet No 4 in A{{music|b}}, op 8 |url=http://www.enspub.com/pages/93/93503.htm |access-date=14 February 2023 |publisher=imslp}}</ref>

Examples of such key signatures are pictured below:
:<score>
\relative c' { \omit Staff.TimeSignature \omit Staff.KeyCancellation
  \key gis \major <gis' bis dis><eis gis bis>_\markup \halign #0.2 \center-column { "G♯ maj" "E♯ min" } \bar "||"
  \key dis \major <dis fisis ais><bis dis fisis>_\markup \halign #0.2 \center-column { "D♯ maj" "B♯ min" } \bar "||"
  \key fes \major <fes' as ces><des fes as>_\markup \halign #0.2 \center-column { "F♭ maj" "D♭ min" } \bar "||"
  \key beses \major <beses' des fes><ges beses des>_\markup \halign #0.2 \center-column { "B♭♭ maj" "G♭ min" }
}
</score>
There does not appear to be a standard on how to notate these key signatures:

* The default behaviour of [[LilyPond]] (pictured above) writes all single sharps or flats in the circle-of-fifths order before showing the double signs. This is the format used in [[John Foulds]]' ''[[A World Requiem]]'', Op. 60, which uses the key signature of G♯ major as displayed above.<ref>{{IMSLP|work=A World Requiem, Op.60 (Foulds, John)|cname=John Foulds: ''A World Requiem'', pp. 153ff.}}</ref> The sharps in the key signature of [[G-sharp major|G♯ major]] proceed C♯, G♯, D♯, A♯, E♯, B♯, F{{music|x}}.
* The single signs at the beginning are sometimes repeated as a courtesy, e.g. [[Max Reger]]'s ''Supplement to the Theory of Modulation'', which contains [[D♭ minor]] key signatures on pp.&nbsp;42–45.<ref>{{cite book |author=Max Reger |title=Supplement to the Theory of Modulation |publisher=C. F. Kahnt Nachfolger |year=1904 |location=Leipzig |pages=[https://archive.org/details/supplementtotheo00rege/page/42/mode/2up 42–45] |translator=John Bernhoff}}</ref> These have a B♭ at the start and also a B{{music|bb}} at the end (with a double-flat symbol), going B♭, E♭, A♭, D♭, G♭, C♭, F♭, B{{music|bb}}.
* Sometimes the double signs are written at the beginning of the key signature, followed by the single signs. For example, F♭ would be notated as B{{music|bb}}, E♭, A♭, D♭, G♭, C♭, F♭. This convention is used by Victor Ewald<ref>[https://www.hickeys.com/music/brass/brass_ensembles/brass_quintets/products/sku035994-ewald-victor-quintet-no-4-in-ab-op-8.php "Ewald, Victor: Quintet No 4 in A{{music|b}}, op 8"], Hickey's Music Center</ref> and by some theoretical works.
* No. 18 of Anton Reicha's ''Practische Beispiele'' in B♯ major<ref name=":0" /> shows B♯, E♯, A{{music|x}}, D{{music|x}}, G{{music|x}}, C{{music|x}}, F{{music|x}}.

In [[tuning system]]s where the number of notes per octave is not a multiple of 12, notes such as G{{music|#}} and A{{music|b}} are not enharmonically equivalent, nor are the corresponding key signatures. These tunings can produce keys with no analogue in 12-tone equal temperament, which can require double sharps, double flats, or [[microtonal music|microtonal alterations]] in key signatures. For example, the key of G♯ major, with eight sharps, is equivalent to A{{music|b}} major in 12-tone equal temperament, but in [[19 equal temperament|19-tone equal temperament]], it is equivalent to A{{Music|bb}} major instead, with 11 flats.

==Major scale structure==
===Scales with sharp key signatures===
There can be up to seven sharps in a key signature, appearing in this order: {{nowrap|F{{music|sharp}} C{{music|sharp}} G{{music|sharp}} D{{music|sharp}} A{{music|sharp}} E{{music|sharp}} B{{music|sharp}}}}.<ref name="Bower">Bower, Michael. 2007. "[http://www.empire.k12.ca.us/capistrano/Mike/capmusic/Key%20Signatures/key_signatures.htm All about Key Signatures] {{Webarchive|url=https://web.archive.org/web/20100311182612/http://www.empire.k12.ca.us/capistrano/mike/capmusic/key%20signatures/key_signatures.htm |date=2010-03-11 }}". Modesto, CA: Capistrano School (K–12) website. (Accessed 17 March 2010).</ref><ref name="Jones">Jones, George Thaddeus. 1974. ''Music Theory: The Fundamental Concepts of Tonal Music Including Notation, Terminology, and Harmony'', p. 35. Barnes & Noble Outline Series 137. New York City, Hagerstown, San Francisco, London: [[Barnes & Noble]]. {{ISBN|978-0-06-460137-5}}.</ref> The key note or [[Tonic (music)|tonic]] of a piece in a major key is a semitone above the last sharp in the signature.<ref name="Kennedy">Kennedy, Michael. 1994. "Key-Signature". ''Oxford Dictionary of Music'', second edition, associate editor, Joyce Bourne. Oxford and New York: Oxford University Press. {{ISBN|0-19-869162-9}}.</ref> For example, the key of D major has a key signature of F{{music|sharp}} and C{{music|sharp}}, and the tonic (D) is a semitone above C{{music|sharp}}. Each scale starting on the [[Perfect fifth|fifth]] [[scale degree]] of the previous scale has one new sharp, added in the order shown.<ref name="Jones"/>
<!--Please do not change the sharp signs to number (#) signs.-->
{| class="wikitable"
|-
! Major key !! Number<br />of sharps !! Sharp notes !! Minor key !! Enharmonic<br />equivalent
|-
| [[C major]] || 0 || – || [[A minor]] ||rowspan="5"| None
|-
| [[G major]] || 1 || F{{music|sharp}} || [[E minor]]
|-
| [[D major]] || 2 || F{{music|sharp}}, C{{music|sharp}} || [[B minor]]
|-
| [[A major]] || 3 || F{{music|sharp}}, C{{music|sharp}}, G{{music|sharp}} || [[F-sharp minor|F{{music|sharp}} minor]]
|-
| [[E major]] || 4 || F{{music|sharp}}, C{{music|sharp}}, G{{music|sharp}}, D{{music|sharp}} || [[C-sharp minor|C{{music|sharp}} minor]]
|-
| [[B major]] || 5|| F{{music|sharp}}, C{{music|sharp}}, G{{music|sharp}}, D{{music|sharp}}, A{{music|sharp}} || [[G-sharp minor|G{{music|sharp}} minor]] || [[C-flat major|C{{music|flat}} major]]/[[A-flat minor|A{{music|flat}} minor]]
|-
| [[F-sharp major|F{{music|sharp}} major]] || 6 || F{{music|sharp}}, C{{music|sharp}}, G{{music|sharp}}, D{{music|sharp}}, A{{music|sharp}}, E{{music|sharp}} || [[D-sharp minor|D{{music|sharp}} minor]] || [[G-flat major|G{{music|flat}} major]]/[[E-flat minor|E{{music|flat}} minor]]
|-
| [[C-sharp major|C{{music|sharp}} major]] || 7 || F{{music|sharp}}, C{{music|sharp}}, G{{music|sharp}}, D{{music|sharp}}, A{{music|sharp}}, E{{music|sharp}}, B{{music|sharp}} || [[A-sharp minor|A{{music|sharp}} minor]] || [[D-flat major|D{{music|flat}} major]]/[[B-flat minor|B{{music|flat}} minor]]
|}

===Scales with flat key signatures===
There can be up to seven flats in a key signature, applied as: {{nowrap|B{{music|flat}} E{{music|flat}} A{{music|flat}} D{{music|flat}} G{{music|flat}} C{{music|flat}} F{{music|flat}}}}<ref name="Bower"/><ref name="Jones"/> The major scale with one flat is F major. In all major scales with flat key signatures, the tonic in a major key is a perfect fourth below the last flat. When there is more than one flat, the tonic is the note of the second-to-last flat in the signature.<ref name="Kennedy"/> In the major key with four flats (B{{music|flat}} E{{music|flat}} A{{music|flat}} D{{music|flat}}), for example, the second to last flat is A{{music|flat}}, indicating a key of A{{music|flat}} major. Each new scale starts a fifth ''below'' (or a [[Perfect fourth|fourth]] above) the previous one.

{| class="wikitable"
|-
! Major key !! Number<br />of flats !! Flat notes !! Minor key !! Enharmonic<br />equivalent
|-
| [[C major]] || 0 || – || [[A minor]] ||rowspan="5"| None
|-
| [[F major]] || 1 || B{{music|flat}} || [[D minor]]
|-
| [[B-flat major|B{{music|flat}} major]] || 2 || B{{music|flat}}, E{{music|flat}} || [[G minor]]
|-
| [[E-flat major|E{{music|flat}} major]] || 3 || B{{music|flat}}, E{{music|flat}}, A{{music|flat}} || [[C minor]]
|-
| [[A-flat major|A{{music|flat}} major]] || 4 || B{{music|flat}}, E{{music|flat}}, A{{music|flat}}, D{{music|flat}} || [[F minor]]
|-
| [[D-flat major|D{{music|flat}} major]] || 5 || B{{music|flat}}, E{{music|flat}}, A{{music|flat}}, D{{music|flat}}, G{{music|flat}} || [[B-flat minor|B{{music|flat}} minor]] || [[C-sharp major|C{{music|sharp}} major]]/[[A-sharp minor|A{{music|sharp}} minor]]
|-
| [[G-flat major|G{{music|flat}} major]] || 6 || B{{music|flat}}, E{{music|flat}}, A{{music|flat}}, D{{music|flat}}, G{{music|flat}}, C{{music|flat}} || [[E-flat minor|E{{music|flat}} minor]] || [[F-sharp major|F{{music|sharp}} major]]/[[D-sharp minor|D{{music|sharp}} minor]]
|-
| [[C-flat major|C{{music|flat}} major]] || 7 || B{{music|flat}}, E{{music|flat}}, A{{music|flat}}, D{{music|flat}}, G{{music|flat}}, C{{music|flat}}, F{{music|flat}} || [[A-flat minor|A{{music|flat}} minor]] || [[B major]]/[[G-sharp minor|G{{music|sharp}} minor]]
|}

== Relationship between key and signature ==
The sharps or flats needed to produce a [[diatonic scale]] in [[diatonic]] or [[tonality|tonal]] music can be shown as a key signature at the beginning of a section of music instead of showing accidentals on individual notes. While the key of a piece generally corresponds to the notated key signature, it may not in some cases, such as in pre-Baroque music, which was composed before the modern concept of keys had fully emerged.

Some pieces feature [[modulation (music)|modulation]]s, or changes in key, between contrasting sections. Modulations may or may not be reflected by a corresponding change in key signature. Modulated passages may instead make use of accidentals.

[[File:GottesZeit.png|400px|thumb|right|[[Gottes Zeit ist die allerbeste Zeit, BWV 106|Bach Cantata 106]] is almost entirely in E{{music|flat}} major, but has only two flats, not three, in the key signature {{audio|GottesZeit.mid|Play}}]]

The [[Toccata and Fugue in D minor, BWV 538]] by [[Johann Sebastian Bach|Bach]] has a key signature with no sharps or flats, indicating that it may be in D, in [[Dorian mode]], but the B{{music|flat}}s indicated with [[Accidental (music)|accidentals]] make the music in D minor.

===Additional terminology===
{{Multiple issues|section=yes|
{{expand section|date=May 2025}}
{{unreferenced section|date=May 2025}}
}}
Keys which are associated with the same key signature are called [[relative minor/major|relative keys]].

When [[musical mode]]s, such as [[Lydian mode|Lydian]] or Dorian, are written using key signatures, they are called ''transposed modes''.

== Use in other traditions <span class="anchor" id="Use outside of the Western common-practice period"></span> ==<!--[[Unusual key signature]] redirects directly here.-->

{{Image frame|content=<score>{
\relative c' {
  \set Staff.keyAlterations = #`((6 . ,FLAT)(2 . ,FLAT)(3 . ,SHARP)) d es fis g a bes c d }}</score>|width=270|caption=D [[Phrygian dominant scale|Freygish]] scale {{audio|D Freygish.mid|Play}}}}

Key signatures are also used in music that does not come from the Western [[common practice period]]. This includes folk music, non-Western music, and Western music from before or after the common practice period.

[[Klezmer]] music uses scales other than diatonic major or minor, such as [[Phrygian dominant scale]]. Because of the limitations of the [[Great Highland Bagpipe]] scale, key signatures are often omitted from written pipe music, which otherwise would be written with two sharps, F{{music|#}} and C{{music|#}}.<ref>
{{cite web |url=http://lilypond.org/doc/v2.12/Documentation/user/lilypond/Bagpipes#Bagpipes |title=GNU LilyPond—Notation Reference |last1=Nienhuys |first1=Han-Wen |last2=Nieuwenhuizen |first2=Jan |author-link1=Han-Wen Nienhuys |author-link2=Jan Nieuwenhuizen |year=2009 |at=2.6.2 Bagpipes |access-date=2010-03-28 |quote=Bagpipe music nominally uses the key of D Major (even though that isn’t really true). However, since that is the only key that can be used, the key signature is normally not written out.}}</ref> (The pipes are incapable of playing F{{music|natural}} and C{{music|natural}} so the sharps are not notated.) 20th century composers such as [[Béla Bartók|Bartók]] and [[Frederic Rzewski|Rzewski]] (see below) experimented with non-diatonic key signatures.

=== Historical notation ===
[[File:Earlykeysig.png|thumb|right|80px|Variant key signatures in a [[Tomas Luis de Victoria|Victoria]] motet. In the ''superius'' (soprano) part the E{{music|flat}} appears first, and in two other parts a flat occurs in two octaves.]]

In music from the Baroque period, it is common to see key signatures in which the notes are annotated in a different order from the modern practice, or with the same note-letter annotated for each octave.

=== Unusual signatures ===
{{unreferenced section|date=May 2025}}
{{further information|Anhemitonic scale#Modes of the ancohemitonic heptatonic scales and the key signature system}}

The 15 key signatures that form diatonic scales are sometimes called ''standard key signatures''. Other scales are written either with a standard key signature and use accidentals as required, or with a nonstandard key signature. Examples of the latter include the E{{music|b}} (right hand), and F{{music|#}} and G{{music|#}}<!--yes, sharp--> (left hand) used for the С diminished (С [[octatonic scale|octatonic]]) scale in Bartók's ''Crossed Hands'' (no. 99, vol. 4, ''[[Mikrokosmos (Béla Bartók)|Mikrokosmos]]''); the B{{music|b}}, E{{music|b}} and F{{music|#}}<!--yes, sharp--> used for the D [[Phrygian dominant scale]] in [[Frederic Rzewski]]'s ''God to a Hungry Child''; and the E{{music|b}} and D{{music|b}} (right hand) and the B{{music|b}}, A{{music|b}}, G{{music|b}} (left hand) in [[György Ligeti]]'s ''Galamb Borong'' (no. 7 from the second book  of the ''Études pour piano''), and B{{music|b}}, E{{music|b}}, D{{music|b}}, G{{music|b}} (both hands) in ''Pour Irina'' (no. 16 from the same work's third book).

There are also examples of conflicting standard signatures, as in:
* no. 3 of [[Sergei Prokofiev]]'s ''[[Sarcasms (Prokofiev)|Sarcasms]]'', op. 17 (three sharps in the right hand, and five flats in the left hand)
* and four numbers of [[György Ligeti|Ligeti]]'s ''[[Études (Ligeti)|Études pour piano]]'':
** no. 1 from the first book (none in the right hand, and five sharps in the left hand)
** no. 10 from the second book (''Der Zauberlehrling''; none in the right hand, and five flats in the left hand in bars 67–87)
** no. 11 from the second book (''En Suspens''; five flats in the right hand and none in the left hand, with the opposite later on)
** no. 12 from the second book (''Entrelacs''; none in the right hand and five flats in the left hand, with the opposite later on)

No sharps or flats in a key signature can indicate that the music is in the key of C major&nbsp;/ A minor, or that the piece is [[Musical mode|modal]] or [[atonality|atonal]] (does not have a key signature). An example is Bartók's [[Piano Sonata (Bartók)|Piano Sonata]], which has no fixed key and is highly chromatic.

== History ==
The use of a one-flat signature developed in the [[Medieval music|Medieval]] period, but signatures with more than one flat did not appear until the 16th century, and signatures with sharps not until the mid-17th century.<ref>"Key Signature", ''Harvard Dictionary of Music'', 2nd ed.</ref>

When signatures with multiple flats first came in, the order of the flats was not standardized, and often a flat appeared in two different octaves, as shown at right. In the late 15th and early 16th centuries, it was common for different voice parts in the same composition to have different signatures, a situation called a '''partial signature''' or '''conflicting signature'''. This was actually more common than complete signatures in the 15th century.<ref>"Partial Signature", ''Harvard Dictionary of Music'', 2nd ed.</ref> The 16th-century motet ''Absolon fili mi'' by [[Pierre de La Rue]] (formerly attributed to [[Josquin des Prez]]) features two voice parts with two flats, one part with three flats, and one part with four flats.

Baroque music written in [[minor key]]s often was written with a key signature with fewer flats than we now associate with their keys; for example, movements in C minor often had only two flats (because the A{{music|flat}} would frequently have to be sharpened to A{{music|natural}} in the [[minor scale|ascending melodic minor scale]], as would the B{{music|flat}}).

== Table ==
{|
|
{| class="wikitable" style="background:white; text-align:center; margin:0.5em auto"
|-
!Key signature
!Major key
!Minor key
|-
| align=center|[[File:Key Signature C major.jpg|100px|C Major key signature]]<br>no sharps or flats
| [[C major]]
| [[A minor]]
|}
{| class="wikitable" style="background:white; text-align:center; margin:0.5em auto"
|-
!Key signature
!Added {{music|sharp}}
!Major key
!Minor key
!Key signature
!Added {{music|flat}}
!Major key
!Minor key
|-
| align=center|[[File:Key Signature G major.jpg|100px|G Major key signature]]<br>1 sharp
| F{{music|sharp}}
| [[G major]]
| [[E minor]]
| align=center|[[File:Key Signature F major.jpg|100px|F Major key signature]]<br>1 flat
| B{{music|flat}}
| [[F major]]
| [[D minor]]
|-
| align=center|[[File:Key Signature D major.jpg|100px|D Major key signature]]<br>2 sharps
| C{{music|sharp}}
| [[D major]]
| [[B minor]]
| align=center|[[File:Key Signature B-flat major.jpg|100px|B-flat Major key signature]]<br>2 flats
| E{{music|flat}}
| [[B-flat major|B{{music|flat}} major]]
| [[G minor]]
|-
| align=center|[[File:Key Signature A major.jpg|100px|A Major key signature]]<br>3 sharps
| G{{music|sharp}}
| [[A major]]
| [[F-sharp minor|F{{music|sharp}} minor]]
| align=center|[[File:Key Signature E-flat major.jpg|100px|E-flat Major key signature]]<br>3 flats
| A{{music|flat}}
| [[E-flat major|E{{music|flat}} major]]
| [[C minor]]
|-
| align=center|[[File:Key Signature E major.jpg|100px|E Major key signature]]<br>4 sharps
| D{{music|sharp}}
| [[E major]]
| [[C-sharp minor|C{{music|sharp}} minor]]
| align=center|[[File:Key Signature A-flat major.jpg|100px|A-flat Major key signature]]<br>4 flats
| D{{music|flat}}
| [[A-flat major|A{{music|flat}} major]]
| [[F minor]]
|-
| align=center|[[File:Key Signature B major.jpg|100px|B Major key signature]]<br>5 sharps
| A{{music|sharp}}
| [[B major]]
| [[G-sharp minor|G{{music|sharp}} minor]]
| align=center|[[File:Key Signature D-flat major.jpg|100px|D-flat Major key signature]]<br>5 flats
| G{{music|flat}}
| [[D-flat major|D{{music|flat}} major]]
| [[B-flat minor|B{{music|flat}} minor]]
|-
| align=center|[[File:Key Signature F-sharp major.jpg|100px|F-sharp Major key signature]]<br>6 sharps
| E{{music|sharp}}
| [[F-sharp major|F{{music|sharp}} major]]
| [[D-sharp minor|D{{music|sharp}} minor]]
| align=center|[[File:Key Signature G-flat major.jpg|100px|G-flat Major key signature]]<br>6 flats
| C{{music|flat}}
| [[G-flat major|G{{music|flat}} major]]
| [[E-flat minor|E{{music|flat}} minor]]
|-
| align=center|[[File:Key Signature of C-sharp major.jpg|100px|C-sharp Major key signature]]<br>7 sharps
| B{{music|sharp}}
| [[C-sharp major|C{{music|sharp}} major]]
| [[A-sharp minor|A{{music|sharp}} minor]]
| align=center|[[File:Key Signature C-flat major.jpg|100px|C-flat Major key signature]]<br>7 flats
| F{{music|flat}}
| [[C-flat major|C{{music|flat}} major]]
| [[A-flat minor|A{{music|flat}} minor]]
|}
|
|}
[[File:Positions of ♯ and ♭ in Key Signatures in 4 Clefs.svg|thumb|center|Positions of ♯ and ♭ in key signatures in 4 clefs. Sharps in the tenor clef are arranged differently to avoid using a ledger line.]]

== See also ==
* [[Key signature names and translations]]
* [[Major and minor]]
* [[Parallel key]]
* [[Relative key]]
* [[Time signature]]
* [[Universal key]]

== References ==
{{Reflist}}

{{Musical key}}
{{Musical notation}}
{{Use dmy dates|date=December 2024}}

{{DEFAULTSORT:Key Signature}}
[[Category:Musical notation]]

[[fi:Sävellaji#Etumerkintä]]