Near keys and far keys · From Zero to Mozart

The circle of fifths isn't just a filing system for key signatures. It's a map of how related two keys are — and that matters, because pieces don't stay in one key. They travel, and they almost always travel to a neighbour.

Neighbours share almost everything

Keys next to each other on the circle differ by exactly one note. C major and G major:

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C major — the F is natural (low 2 on the D string).

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The same eight letters read in G major — only the F changed, to F♯ (high 2). One note different out of seven. C and G are next-door neighbours.

Keys on opposite sides of the circle — a tritone apart, like C and F♯ — share almost nothing, and a jump between them sounds jarring and remote. Composers use that on purpose, but rarely.

The dominant is the nearest neighbour — and where pieces go

A key's closest relative, one step clockwise, is its dominant (G is the dominant of C). So when a piece leaves home, the dominant is the natural first stop — one note changes, and the ear follows easily.

This is the missing "why" behind something from Stage 3. A minuet's first half often ends with a repeat sign, on a chord that isn't home. That's because the first half has travelled one step clockwise, to the dominant — and the second half brings it back. The double bar isn't the end of a thought; it's the far point of a round trip.

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A little phrase in G major that lands and stops on A — the second degree, part of the dominant chord. It doesn't sound finished; it sounds like a comma. That 'not home yet' feeling is what a piece exploits when it moves to the dominant.

How you spot a key change

Two tells, and you use both:

A new accidental keeps appearing. A tune in G major that suddenly has a C♯ in bar after bar hasn't borrowed one note — it's moved to D major (where C♯ belongs).
A cadence lands in the new key. The phrase comes to rest on a different home note. (Cadences get their own movement.)

Try it

Try

Play a G major scale. Now play it again, but raise every C to C♯ (high 2 on the A string instead of low 2). You've just shifted the whole scale into D major — one note changed, one step clockwise on the circle. Play the two versions back to back and hear the second one lift.

The usual mistake

Reading a piece note by note and never noticing it has changed key — then being surprised when a note "sounds wrong" that's actually right in the new key. Watch for a new accidental that stops being an accident and starts being the rule. That's the music telling you it has moved house, usually to the key next door.