# Diminished/Half diminished

In jazz notation, the degree sign means a diminished chord, for instance CEbGb. A diminished 7 chord would be CEbGbBb? A half diminished chord, a degree sign with a slash, would be what? How do you diminish a diminished chord even more? Does the sign only refer to the 7?

• I am voting to reopen because this question is specifically about diminished and half diminished chords, not about constructing different types of chords in a given key. Commented Jul 18 at 5:19
• @JohnBelzaguy The answer to this question is exactly contained in this answer to the duplicate question. Commented Jul 18 at 8:14
• @Aaron it is in there but the difference is not clearly shown or explained. Commented Jul 18 at 13:07
• Five answers, two upvotes... Answers should automatically count as a question upvote. If it's worth answering, it can't be a bad question. Commented Jul 18 at 16:54
• @piiperiReinstateMonica I have made this point before, people want to answer questions and receive upvotes but don’t bother upvoting the questions they answer. Commented Jul 18 at 16:57

Diminished 7 means that the 7th part is also diminished. So with C°7, the notes are in fact C, E♭, G♭, B♭♭. That last note is often mistakenly known as A.

A half diminished chord, on the other hand, Cø also known as Cm7♭5, has the same base triad, but has B♭ as its fourth note. So, not a fully diminished chord, but known as a half-diminished.

A diminished triad is root, minor 3rd, diminished 5th. C, E♭, G♭.

A diminished 7th chord is all that plus the diminished 7th. C, E♭, G♭, B♭♭.

A half-diminished 7th (often notated as 'm7♭5') is a diminished triad plus the minor 7th. C, E♭, G♭, B♭.

Formulation #1 (stacks of thirds)

A fully diminished seventh chord comprises a stack of three minor thirds.

A half diminished seventh chord comprises a stack of two minor thirds and a major third.

Formulation #2 (intervals above the root)

A fully diminished seventh chord comprises, above the root, a minor third, diminished fifth, and diminished seventh.

A half diminished seventh chord comprises, above the root, a minor third, a diminished fifth, and a minor seventh.

Strictly speaking, there are three chords under discussion:

• the diminished triad (minor third and diminished fifth, for example, C-E♭-G♭)
• the diminished seventh chord (diminished triad plus a diminished seventh, for example C-E♭-G♭-B♭♭)
• the half diminished seventh chord (so called because it has one diminished interval instead of two, it is a diminished triad plus a minor seventh, for example C-E♭-G♭-B♭)

The diminished triad and diminished seventh chord are so similar in sound and function that people often use "diminished chord" for "diminished seventh chord," even though "diminished chord" should really be synonymous with "diminished triad," just as "major chord" and "minor chord" are synonymous with "major triad" and "minor triad," respectively.

There is no such thing as a half-diminished triad, which makes it even more tempting to call the half-diminished seventh chord a "half-diminished chord," but as your question shows, that name leads to some confusion. I always use the full name, "half-diminished seventh chord," to help avoid the confusion.

The other answers are missing the fundamental aspect of musical intervals that is part of source of your confusion.

Read the wiki article on intervals for a detailed description. But, the essentials idea is an interval is given in two parts: a number for the steps between pitch letters and a quality for the exact number of half steps between the intervals.

Now we have the basis for explain the intervals of the third, fifth, and seventh.

I'll skip over the third, because I imagine you already understand that.

A fifth starts with two letters five steps apart, ex. `C` up to `G`. A perfect fifth is a fifth with seven half steps between the pitches. Now, start with `C` and `G`, a fifth but lower the `G` to `Gb`. That is still a fifth, but because there are only six half steps between the pitches it is now a diminished fifth. This type of diminished fifth is what gives the name to various diminished chords.

Follow the same login for sevenths. `C` up to `B` is a seventh. The various qualities of sevenths include: major, minor, and diminished. Their sizes in half steps are respectively 11, 10, and 9. Each will always be spelled, in this example case, with a `C` and `B`. You must use flats to get the various qualities: `B♮`, `B♭`, `B𝄫` (the last one is `B` double flat.) So, a diminished seventh is `C` up to `B𝄫`.

The naming of triads and seventh chords doesn't list all the intervals comprising the chords. Ex. major triad refers to the major third of the chord, but doesn't mention the perfect fifth. Or, diminished triad refers to the diminished fifth, but doesn't mention the minor third. It's not a perfect naming system. The same issue arises with seventh chords.

A diminished seventh chord is a diminished triad plus a diminished seventh.

A half diminished seventh chord is a diminished triad plus a minor seventh.

If you really want to know what "diminished" in those chord names refers to, I think first look at the diatonic seventh chord names:

• Major seventh chord = major triad plus major seventh
• Minor seventh chord = minor triad plus minor seventh
• Dominant seventh chord = major triad plus minor seventh
• Half diminished seventh chord = diminished triad plus minor seventh

By that reckoning the only "half" of the formula which is diminished in a half diminished seventh chord is the triad portion. Maybe it should be called diminished (plus) minor seventh chord. Maybe dominant seventh chords should be called major (plus) minor seventh chords, or half major seventh chords, but they aren't. The system isn't perfect. You must learn the various chord type names and their interval formulas.

...a diminished chord, for instance `C E♭ G♭`

Yes.

...A diminished 7 chord would be `C E♭ G♭ B♭`?

No.

That is a diminished triad plus a minor seventh. So it is a half diminished chord.

To make those pitch letters a fully diminished seventh chord you need a diminished seventh interval which is `C` up to `B𝄫`. The full chord spelling would be `C E♭ G♭ B𝄫`.

That double flat is the source of a lot of confusion for beginners. Especially when lots of beginning theory tries to make things easy by working in `C` major or a chord root of `C` for many lessons. If you actually encounter the diminished seventh chord `C E♭ G♭ B𝄫`, its most basic appearance would be in the key of `D♭` major. Actually, diminished seventh chords are in a basic sense associated with minor keys, which would be that key should be `D♭` minor, a theoretical key that is not normally used. `C♯` minor would normally be used instead and the diminished seventh chord would then be respelled for that key as `B♯ D♯ F♯ A`, which avoids the double flat but isn't much easier to read.

Notice how we've descended into a thicket of confusing theory and enharmonic respellings?

We can avoid all that by putting diminished seventh chords in context of their position in keys. It's probably easiest to look at both diminished seventh chords and half diminished chords used simultaneously through minor keys. Choose either `A` minor or `C` minor to keep things simple.

The diminished seventh chord will be rooted on the leading tone in minor. In scale degrees it will be `^7 ^2 ^4 ^6`, and the only accidental needed will be to raise the `^7`. Ex. in `A` minor: `G# B D F`. Ex. in `C` minor: `B♮ D F A♭` (Notice the flat on the `A` does not require an accidental as it is already in the key signature.)

The half diminished seventh chord will be rooted on the second scale degree in minor. In scale degrees it is `^2 ^4 ^6 ^1` and no accidentals are needed. Ex. in `A` minor: `B D F A`. Ex. in `C` minor: `D F A♭ C`.

In Roman numeral analysis the two chords are labelled `viio7` and `iiø7`.

Take some time at a keyboard to examine those chord within those keys. Take note of the scale degrees, which scale degrees require accidentals, the chord intervals, and the number of half steps within each of those intervals. Take heart that if you look at those two types of diminished seventh chords in minor keys only one accidental is needed to spell them in all keys, all the other sharps/flats come from the key signatures.

And finally, because you mentioned jazz, there are two ways the half diminished seventh chord is commonly labelled with jazz/pop chord symbols: `m6` and `m7♭5`. In "classical" theory those two chords are consider inversions of the same chord type (half diminished seventh chord), but jazz sort of uses them interchangeable. Our previous `Cm: iiø7` - pitches `D F A♭ C` - in jazz/pop symbols would be either `Fm6/D` or `Dm7♭5`. If the pitches are reordered to `F A♭ C D` the jazz/pop symbols would be `Fm6` or `Dm7♭5/F`. The `/D` and `/F` denote the pitch in the bass for jazz/pop chord symbols.

A diminished seventh chord consists of the root, minor third, diminished fifth and diminished seventh: C, Eb, Gb, Bbb.

Cdim7:

A half-diminished seventh chord has a diminished fifth, but the seventh is not diminished: C, Eb, Gb, Bb.

Cm7b5:

Ah, really good question. Diminished chord/triad: 1 b3 b5, and Half-diminished chord: 1 b3 b5 b7. Why Does not recongnise this 1 b3 b5 bb7 for diminished chord, Because this 1 b3 b5 bb7 it is not for meantone system thinking.

• What is "meantone system thinking"? Commented Jul 19 at 18:16
• In meantone system, For example, In the Root of C, C Eb Gb Bbb is not B# D# F# A, Is has a diesis between the two notes, If you making this C Eb Gb Bbb and B# D# F# A are sound the same chord, the diesis should be tempered out(or vanish). So, the diminished 7th chord are not fits in meantone system, and augmented triad (1 3 #5) are not fits in meantone system either. Commented Jul 19 at 20:08
• I am suddenly inspired to see how modulation using enharmonically reinterpreted diminished seventh chords would work on a keyboard with split sharps/flats. Commented Jul 22 at 19:22

The diminished seventh chord refers to the interval of the seventh note in the chord. It is a diminished seventh above the root.

The half diminished chord has a root, minor third, and diminished fifth, and minor seventh, while the diminished seventh chord has those same notes except for the minor seventh which is lowered a further semitone to make it a diminished seventh interval.

So for example c half diminished would consist of C-Eb-Gb-Bb while the diminished seventh chord built on C would consist of C-Eb-Gb-Bbb.

There is actually just one semitone between the two chords.

• "The diminished seventh chord refers to the interval of the seventh note in the chord": if this were true then changing the diminished seventh to a minor seventh would not result in a "half-diminished seventh chord." Commented Jul 22 at 18:37