Chords in a key where the roots come from

A key is a scale, and stacking thirds on each note of that scale gives seven chords that belong together. Number them and every song in every key reads the same. For a bass player the number is a map: it tells you which root to play next and how far to move — the same distance in every key. That is how you follow a chart you have never seen, and guess the next change before the band plays it.

Seven chords from one scale

Build a triad on each note of the major scale using only notes from that scale. The qualities always fall in the same order:

I major · ii minor · iii minor · IV major · V major · vi minor · vii° diminished

Capital numerals are major, small ones minor, ° diminished. In E that is E · F♯m · G♯m · A · B · C♯m · D♯°. You play the root of each, so the letters are your notes; the quality only decides which third you reach for when you leave the root.

The keys you will meet first

Read down a column to move a song: the IV of every key, the V of every key.

Key	I	ii	iii	IV	V	vi	vii°
E	E	F♯m	G♯m	A	B	C♯m	D♯°
A	A	Bm	C♯m	D	E	F♯m	G♯°
D	D	Em	F♯m	G	A	Bm	C♯°
G	G	Am	Bm	C	D	Em	F♯°
C	C	Dm	Em	F	G	Am	B°

One string, three numbers

On any one string, the IV is five frets above the I and the V is seven. Open E, fret 5, fret 7 is E, A, B — the I, IV and V of E. Open A, fret 5, fret 7 is A, D, E. The shape never changes; only where you start does.

G|------------|
D|------------|
A|------------|
E|--0--5--7--0|
    E  A  B  E

Start on the A string and the same three frets give you the key of A:

G|------------|
D|------------|
A|--0--5--7--0|
E|------------|
    A  D  E  A

Or keep the key of A on the E string by starting at fret 5 — the IV is fret 10 and the V is fret 12:

G|------------|
D|------------|
A|------------|
E|--5-10-12--5|
    A  D  E  A

Progressions by number, as roots

The same few number patterns run through most popular music. Each is in E, one root a half note, two to a bar. Say the number as you play it.

I – IV – V – I — E A B E

Folk, country, rock and roll — the three-chord song.

G|------|------|------|------|
D|------|------|------|------|
A|------|--0--0|--2--2|------|
E|--0--0|------|------|--0--0|
    E      A      B      E

I – V – vi – IV — E B C♯m A

The pop loop under hundreds of songs.

G|------|------|------|------|
D|------|------|------|------|
A|------|--2--2|--4--4|--0--0|
E|--0--0|------|------|------|
    E      B    C#m      A

vi – IV – I – V — C♯m A E B

Same four chords, starting on the minor — it sounds sadder.

G|------|------|------|------|
D|------|------|------|------|
A|--4--4|--0--0|------|--2--2|
E|------|------|--0--0|------|
  C#m      A      E      B

I – vi – IV – V — E C♯m A B

The 1950s doo-wop turn.

G|------|------|------|------|
D|------|------|------|------|
A|------|--4--4|--0--0|--2--2|
E|--0--0|------|------|------|
    E    C#m      A      B

ii – V – I — F♯m B E

The jazz cadence, as three bars of roots — Walking bass fills them in.

G|------|------|------|
D|------|------|------|
A|------|--2--2|------|
E|--2--2|------|--0--0|
  F#m      B      E

Root and fifth

The first thing a bass adds to a root is the fifth: from any root, go one string up and two frets up. It is the same shape from every root, so you can play the I–IV–V–I above as root, fifth, root, fifth and never leave the first five frets. Say the chord, then the number, then the note.

G|------|------|------|------|
D|------|-----2|-----4|------|
A|-----2|--0---|--2---|-----2|
E|--0---|------|------|--0---|
    E  B   A  E   B F#   E  B

Play it in Grooves & pocket rhythms next, or write it over a song on Write grooves over songs.

Why V wants to go home

The V chord holds the scale’s seventh note, a half step under the root, and that note wants to rise. On a V chord that note is the third: in B it is D♯, and it steps up to E. You feel it as a root that wants to fall a fifth, from B down to E — the strongest move in the key. Play B, then the half-step lean D♯, then home.

G|---------|
D|-----1--2|
A|--2------|
E|---------|
    B D#  E

Minor keys

Every major key has a relative minor on its vi: C♯m for E, Am for C. Same seven chords, different home — the song sounds minor when it starts and ends on the vi, so your lowest note is the vi root. Minor-key songs usually borrow a major V (B in C♯ minor) for the pull home, which comes from the harmonic minor on Scales.

Find the key of a song

Write down every chord in the song, or the root you play under each one.
Find the row in the table that holds all of them. That is the key (or its relative minor).
The chord the song ends on — and usually starts on — is home.

Try it: E A B C♯m → E. G C D Em → G. Am F C G, ending on Am → A minor, relative of C.

Ready when

Move on when all of these are true on a normal day, not your best one:

You can play I, IV and V of E, A, D and G on one string without the table.
Given a chord list, you can name the key and play the roots in another key.
You can play the root and the fifth under any chord of a I–V–vi–IV loop, and hear when the V is about to land.

Sources: standard diatonic triads and Roman-numeral analysis, the same as the Guitar page. Every spelling is checked against the major scale in its key; the frets are checked against standard tuning, E A D G.

Text twin: keys.md