How do key signatures work, and how does the circle of fifths organise every major and minor key?
Identify and write the key signatures for every major and minor key and use the circle of fifths to relate keys and find relative and parallel keys
Key signatures fix the sharps or flats of a key in a set order. The circle of fifths arranges all twelve major and minor keys by the number of accidentals, and shows relative, parallel and closely related keys at a glance.
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What this dot point is asking
You need to write the correct key signature for any major or minor key, name the key from a given signature, and use the circle of fifths to relate keys to one another. This underpins transposition, harmony, analysis and modulation.
What a key signature does
Rather than writing an accidental every time a note needs to be sharpened or flattened, a key signature states the sharps or flats once at the beginning of every stave. Every C major scale has no accidentals, so C major (and its relative A minor) has an empty key signature. G major needs F sharp, so its signature is one sharp. The signature saves clutter and signals the tonal centre of the music to the reader.
The order of sharps and flats
Sharps are always added in the fixed order F C G D A E B. A common memory aid is the sentence about a battle ending and victory finally. Flats follow the exact reverse, B E A D G C F, which conveniently spells two real words. Because the order never changes, if a signature has three sharps they must be F sharp, C sharp and G sharp, giving A major.
The circle of fifths
The circle of fifths places C major at the top with no accidentals. Moving clockwise in perfect fifths (C, G, D, A, E, B, F sharp) adds one sharp each time. Moving anticlockwise in perfect fourths (C, F, B flat, E flat, A flat) adds one flat each time. After six steps the sharp and flat keys meet at enharmonic equivalents such as F sharp major and G flat major. The circle is the single most efficient summary of how keys relate.
Relative, parallel and closely related keys
- Relative keys share a key signature: every major key has a relative minor a minor third below it (C major and A minor share no accidentals).
- Parallel keys share a tonic but differ in mode (C major and C minor); they have different signatures.
- Closely related keys sit next to each other on the circle and differ by no more than one accidental, which is why music modulates most often to the dominant, subdominant or relative.
Minor keys on the circle
Each point on the circle carries both a major key and its relative minor on an inner ring. A minor sits with C major, E minor with G major, and so on. The harmonic and melodic minors raise the seventh (and sixth) with accidentals written into the music, not into the signature, so a piece in A minor still shows no key signature but adds a G sharp as an accidental.
Why this matters
The circle of fifths is the map of tonal music. It tells you instantly how many accidentals a key has, which keys are closely related for modulation, and where relative and parallel keys sit. In harmony and analysis you use it to explain key changes; in transposition you use it to move between keys; in composition you use it to choose convincing key relationships. Memorise the circle in both directions and the rest of theory falls into place.
Exam-style practice questions
Practice questions written in the style of SACE Board exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
2024 SACE Stage 22 marksWrite the key signature for E flat major in the treble clef, then name its relative minor.Show worked answer →
Two marks: one for the correct key signature, one for the relative minor.
E flat major has three flats. Using the fixed order of flats B E A D G C F, take the first three, B flat, E flat and A flat, and write them in that order on their correct stave positions. To check, the second-to-last flat names the major key, and the second-to-last of B, E, A is E, confirming E flat major.
For the relative minor, count down three semitones (a minor third) from E flat to C, so the relative minor is C minor, which shares the same three flats. Markers require both the accidentals in the correct order and positions and the correct relative minor.
2023 SACE Stage 22 marksA piece has four sharps in its key signature. Name the major key and its relative minor, and explain how you identified the major key from the signature.Show worked answer →
Two marks: one for naming both keys, one for explaining the method.
Four sharps, in the fixed order F C G D A E B, are F sharp, C sharp, G sharp and D sharp. For sharp keys the last sharp is the leading note, so go up one semitone from the last sharp (D sharp) to reach the tonic, E, giving E major.
The relative minor is a minor third below the major tonic: down three semitones from E gives C sharp minor, sharing the same four sharps. A full-mark answer states E major and C sharp minor and explains the last-sharp-plus-a-semitone rule rather than just naming the key.