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

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.