Key Relationships and the Circle of Fifths

At this point twelve major and twelve minor keys are available — twenty-four in total. This lesson is about how they relate to one another.

The short answer is that closeness between keys is measured by how many notes they share. The diagram that organizes all of those relationships at once is the circle of fifths.

The circle of fifths — ordering by perfect fifths

The circle of fifths arranges the twelve keys around a clock face. There is exactly one rule for the ordering: each step clockwise goes up a perfect 5th.

Starting at C, a fifth up is G, then D, then A, E, B, F♯, and after twelve steps you are back at C.

Stacking fifths all the way around

▶Six fifths up▶Fifths downward

Check: These climb by perfect fifths from C. Take it slowly and confirm that every adjacent pair carries the same sense of distance. Twelve of those steps land back on C, several octaves higher — and that is what makes the circle close.

C→G→D→A→E→B

Why fifths in particular? Because, as the previous unit established, each step of a fifth changes the key signature by exactly one accidental.

• clockwise (up a fifth) → one more sharp
• counterclockwise (down a fifth) → one more flat

So distance on the circle is the difference in key signature, and that in turn is the difference in shared notes. Neighboring keys differ by exactly one note.

Check

How many notes do C major and D major (two sharps) share?

5476

Check answer

Four named relationships

Four relationships among the twenty-four keys have names of their own. Taking C major as the reference point:

Relationship	Key	Difference in signature	Shared notes
Relative	A minor	0 (identical)	7 (all of them)
Dominant	G major	1	6
Subdominant	F major	1	6
Parallel	C minor	3	4

Relative keys

A major and a minor key that share a key signature. They use identical notes and differ only in which one is the tonic. The relative minor’s tonic lies a minor 3rd below the major tonic.

C major ⇄ A minor, G major ⇄ E minor, F major ⇄ D minor.

Since you can move between them without altering a single note, this is the closest relationship there is. Music takes constant advantage of it — a middle section of a major-key piece shifting into the relative minor is one of the most common formal moves in the repertoire.

Dominant and subdominant keys

The key a perfect 5th above the tonic is the dominant key; the key a perfect 5th below (equivalently a fourth above) is the subdominant. On the circle they are the clockwise and counterclockwise neighbors.

Both share six notes, differing by one. That proximity makes them the most natural destinations for a modulation. The classical convention of presenting a sonata-form second theme in the dominant key is built on exactly this closeness.

Parallel keys

Same tonic, different mode — C major and C minor. Their signatures differ by three accidentals, so they share only four notes, which puts them further away than the dominant on the shared-note measure.

And yet real music swaps between parallel keys constantly. The reason is that the tonic does not move. The center of the key stays exactly where it was while the major/minor coloring flips, so a listener receives a dramatic change without losing their bearings.

Which shows that shared notes are not the only measure of closeness. There is a second axis — whether the tonic is preserved — and parallel keys are close on that one. The distinction between these two axes becomes important in Unit 8, in the treatment of borrowed chords and modulation.

The four relationships as chord moves

▶C → relative A minor▶C → dominant G▶C → subdominant F▶C → parallel C minor

Check: Each starts on the C major triad and moves to the tonic chord of one related key. The relative minor barely leaves the room; the dominant feels like stepping next door; the parallel minor stays in place and inverts the color. The kinds of closeness are genuinely different from each other.

signature difference 0 — same notes

Check

What is the relative key of D minor?

D majorF majorA minorBb major

Check answer

Enharmonic keys meet at the bottom of the circle

Going clockwise adds sharps and going counterclockwise adds flats. Follow both directions far enough and they meet at the bottom of the circle, around six o’clock.

What sits there is F♯ major (six sharps) alongside G♭ major (six flats) — the enharmonic keys from Unit 0, identical in sound and different in spelling.

That meeting is what allows the circle to close. Without treating enharmonics as equivalent, stacking fifths would never return to the original C. In fact, twelve pure fifths overshoot the starting pitch slightly, so the shape would be a spiral rather than a circle. Equal temperament and enharmonic equivalence are what bend the spiral into a circle.

Closeness is ease of modulation

The practical value of the circle is that it works as a map for modulation.

• adjacent keys (dominant, subdominant) share six notes, so you can arrive almost without preparation
• the relative key requires changing no notes at all, only relocating the center
• distant keys (three or more steps around) need an intermediate stop or a shared chord to act as a hinge

Unit 8 covers how those distances actually get crossed. What matters at this point is having the map. Closeness has stopped being a vague impression and become something you can count.

▶ Work with the circle directly Tapping a key shows its signature, its diatonic chords, and its relative key. Move to an adjacent key and confirm that exactly one note changes Circle of Fifths → ▶ Or go the other way and infer a key from chords Enter a progression and it offers candidate keys. Several candidates appear at once precisely because closely related keys share so many notes — the closeness in this lesson is the same thing as the ambiguity Key Finder →

That completes Unit 2. The next unit stacks the notes of a scale into chords. The scale degrees and the map of keys developed here become the foundation for chord names and chord functions alike.