Chord Naming Guide

The Basic Idea

Most chord symbols start from a stack of thirds. Pick a candidate root, then lay out the chord-member letter names above it:

The numbers do not describe register. In chord-symbol language, a D right next to middle C and a D two octaves higher are both the ninth above C. The stack is a naming map: each letter slot has a default quality, and the actual note either matches that default or alters it.

Default Interval Qualities

The plain degree numbers in the stack name the positions: third, fifth, seventh, ninth, and so on. They do not by themselves tell you the final accidental. The note letter comes from the position in the stack, and the interval quality tells you whether that letter is natural, lowered, or raised.

Above C, for example, the seventh slot is always some kind of B. B is the major seventh, B♭ is the minor seventh, and B𝄫 is the diminished seventh. It does not become A just because it has been lowered; changing the letter would move it into a different slot.

Chord symbols have defaults for those interval qualities.

Chord member	Default above C	Lowered	Raised
3rd	E, major	E♭, minor (m)	E♯, augmented*
5th	G, perfect	G♭, diminished (♭5, dim)	G♯, augmented (♯5, aug)
7th	B♭, minor (7)	B𝄫, diminished (dim7)	B, major (maj7)
9th	D, major	D♭, minor (♭9)	D♯, augmented (♯9)
11th	F, perfect	F♭, diminished*	F♯, augmented (♯11)
13th	A, major	A♭, minor (♭13)	A♯, augmented*

* Chord symbols never use these three qualities. Each is enharmonically a plainer chord member, so the simpler spelling always wins: a raised 3rd (E♯) is the perfect 11th (F), a lowered 11th (F♭) is the major 3rd (E), and a raised 13th (A♯) is the minor 7th (B♭).

The third is major by default, unless m makes it minor. The fifth and eleventh are perfect by default, unless altered. Every default here matches the major scale except the seventh: the bare 7 means the lowered, minor seventh, so C7 is C-E-G-B♭, not C-E-G-B. The word maj changes only that seventh, so Cmaj7 means C-E-G-B, while Cm7 changes the third to E♭ but leaves the seventh at its default B♭.

Diminished and augmented are interval qualities too. A diminished interval is one semitone smaller than minor or perfect. An augmented interval is one semitone larger than major or perfect. Chord labels use those interval qualities as shortcuts: Cdim means a minor third plus a diminished fifth, C-E♭-G♭. Cdim7 adds a diminished seventh, B𝄫. A half-diminished seventh chord, Cm7(♭5), keeps the default minor seventh and lowers only the fifth. Caug means an augmented triad: C-E-G♯.

From Degrees to Quality Names

Once the notes are mapped to degree numbers, the chord quality comes from the pattern those degrees make. A few common patterns do most of the work:

Quality	Degree formula	Example on C
Major triad	1 3 5	C = C-E-G
Minor triad	1 ♭3 5	Cm = C-E♭-G
Diminished triad	1 ♭3 ♭5	Cdim = C-E♭-G♭
Augmented triad	1 3 ♯5	Caug = C-E-G♯
Dominant seventh	1 3 5 ♭7	C7 = C-E-G-B♭
Major seventh	1 3 5 7	Cmaj7 = C-E-G-B
Minor seventh	1 ♭3 5 ♭7	Cm7 = C-E♭-G-B♭
Half-diminished seventh	1 ♭3 ♭5 ♭7	Cm7(♭5) = C-E♭-G♭-B♭
Fully diminished seventh	1 ♭3 ♭5 𝄫7	Cdim7 = C-E♭-G♭-B𝄫
Dominant ninth	1 3 5 ♭7 9	C9 = C-E-G-B♭-D
Added ninth	1 3 5 9	Cadd9 = C-E-G-D

Extensions vs. Added Tones

A seventh turns upper notes into extensions. With the seventh present, D above C is a ninth, F is an eleventh, and A is a thirteenth. Without the seventh, those same notes are added tones or sixths: C9 includes B♭, while Cadd9 does not.

The thirteenth has one common naming exception. If there is no seventh, an A above C is written as a sixth: C6. Add the seventh and that same chord member becomes a thirteenth: C13.

Slash Bass

The bass note is the lowest sounding note. When the bass is not the root of the chord name, chord symbols write it after a slash: C9 / E means C dominant ninth with E in the bass. The slash note is not a second chord, and it does not change the root. It only tells the player what note is underneath the chord.

If the bass is already the root, no slash note is needed. A C dominant ninth with C in the bass is simply C9, not C9 / C.

How to Name a Chord

A practical naming pass looks like this:

1. List the sounding pitch classes and the bass note. Ignore doublings, but keep the lowest note for slash-bass decisions.
2. Try candidate roots. Usually those are notes already present in the chord, plus obvious enharmonic spellings when they make the tertian stack cleaner.
3. For each root, write the 1 3 5 7 9 11 13 letter stack.
4. Place each sounding note into its letter slot, respelling enharmonically when the chord function demands it.
5. Prefer names with a clear triad or seventh-chord base, fewer awkward alterations, and no unnecessary slash bass.

The result is not always unique. Some pitch sets really do have several good names, and musical context may decide between them. But this process gives you a disciplined way to find the names that are musically defensible before choosing the most readable one.

Worked Example

Suppose the sounding notes are C, E, G, B♭, and D, with C in the bass. The goal is to work from the notes toward a name, not to assume the name first. C is a good root to test because it is in the bass, and the notes above it include the familiar C-E-G shape.

Start by stacking thirds above C through the ninth:

Now compare the sounding notes to those slots. C, E, and G give a major triad because the third is E, not E♭. The seventh slot above C is some kind of B; the sounding note is B♭, which is the default minor seventh. A major triad plus the default minor seventh is written C7, not Cm7, because nothing has made the third minor. D is in the ninth slot. Because the seventh is present, that D is an extension rather than an added tone.

That points to C9: the seventh is present, so it is not Cadd9, and the bass is C, so no slash note is needed. Before committing to it, though, a thorough pass should weigh the other roots.

Trying Other Roots

For this note set, the candidate roots are the notes that are actually sounding: C, E, G, B♭, and D.

Try E next. The letter stack above E is E-G-B-D-F-A-C. The sounding notes then map as E, G, B♭, D, and C:

That gives an E half-diminished seventh shape: 1 ♭3 ♭5 ♭7. The remaining C is the lowered thirteenth above E, but because it is also the bass, slash notation can account for it: Em7(♭5) / C. That is valid, but it is already more complex than the C-rooted name: it needs an altered fifth and slash bass, while the C reading gave a direct dominant ninth.

Doing the same check for each sounding note gives this comparison:

Root tested	Note names in stack order	Degree numbers	Candidate name
C	C E G B♭ D	1 3 5 ♭7 9	C9
E	E G B♭ D C	1 ♭3 ♭5 ♭7 ♭13	Em7(♭5) / C
G	G B♭ D C E	1 ♭3 5 11 13	Gm6 / C
B♭	B♭ D C E G	1 3 9 ♯11 13	B♭6♯11 / C
D	D C E G B♭	1 ♭7 9 11 ♭13	D9sus4(♭13) / C

Those names are not equally useful. The C reading has a complete, familiar base chord: 1 3 5 ♭7, then one ordinary ninth. The alternatives need more explanation: they lack a complete triad or seventh-chord base, depend on several upper extensions or altered degrees, or require slash bass to account for C underneath them.

The C reading wins because it has the strongest base chord, the bass is the root, and the remaining note has a standard name as a ninth. Deciding which reading is "best" can still be tricky, especially in real music where context matters, but this is the kind of comparison that makes one option much easier to justify than the others.

Why Spelling Matters

The spelling is not cosmetic. In this example, B♭ is the seventh above C. Spelling the same physical piano key as A♯ would make it look like some kind of altered sixth instead of the chord's seventh. Both spellings represent the same pitch class, but chord symbols use enharmonic spelling to show function, not just keys on the instrument.

How WhatChord Uses This Idea

WhatChord evaluates candidate roots and qualities in software rather than by hand. It scores candidates for musical strength: stable triads and seventh chords, sensible extensions, spelling that fits the chord member, and bass relationships that musicians expect to read. Close alternatives can still appear when the notes genuinely support more than one interpretation.

The app asks the same questions a player asks: What is the root? What is the base quality? Which notes are extensions or alterations? Is the bass part of the chord or a slash note? Which spelling makes the stack readable?

For the implementation details behind those scores, see Building a Real-Time Chord Recognizer.

Acknowledgements

This guide was inspired in part by discussion with u/MaggaraMarine, who pointed toward clarifying default interval qualities behind chord symbols, and u/65TwinReverbRI, whose examples helped motivate the focus on tertian spelling and systematic root checking.