The Diminished Triad and it's 7th chord variants have quite a tense sound.

While at first they may seem to be too dissonant to be used in a scale, in fact they are very versatile and handy chords.

But how do they work? When can we use them? Let's find out.

Understanding diminished chords

If you've learned your Triads, then you'll already know how to make the Diminished Triad, seen here.

That's a Minor 3rd and Tritone building off of the root note of the chord. It can also be helpful to think of it as a series of Minor 3rds.

This triad is found naturally occurring when building a chord from the 7th note in the Major scale, or the 2nd note of the Minor Scale. Refer to Major Diatonics, if needed.

The Diminished triad

Guitar chord diagram showing a diminished chord with intervals notated.

To be honest, this triad doesn't see much use in styles that mostly stick to simple Major and Minor Chords. That rules out most of pop and radio-friendly rock. We're more likely to see it crop up as a 7th chord.

(There's definitely some exceptions, though! Like "All Star" by Smash Mouth of all things...)

Still, we want to know how this triad is built to make sense of the more complex forms of the chord.

Let's take it further, though. This is known as a Half-Diminished 7th chord.

Now we have a Minor 3rd, a Tritone, and a Minor 7th on top.

It's like a Minor 7th Chord with a flattened 5th.

This is the natural result of building a 7th chord off of the 7th note of the Major Scale, or 2nd note of the Minor Scale, just like before.

The half-Diminished 7th chord

Guitar fretboard diagram showing notes on strings with black and gray circles indicating specific notes, including B flat 7, B flat 5, B flat 3, and a red circle with the number 1.

That's not a very functional way to play the chord, so let's look at some shapes we can use, on the E, A, and D strings:

Guitar tablature displaying finger positions for a scale or chord, with fret numbers and note names, including black and gray dots marking specific notes.

Assuming our root note is C, this chord will be notated either as Cø7, or just Cø. Take note of that special symbol!

You might also see the notation "Cm7b5", i.e., Minor 7th with a flat 5th. It means the same thing.

To me, the Half-Diminished chord sounds softer than the Diminished Triad alone. The addition of the Minor 7th interval makes it feel a little less tense and a little more jazzy.

Since this chord is diatonic, naturally occurring on the 2nd note of the Minor Scale, it sees a lot of use when 7th chords are involved.

For example, playing a "2-5-1" chord progression in the Minor Scale with 7th chords will include it. Here's an example using:

Eø7 - A7 - Dm9

Sheet of sheet music with musical notes and chords.

Now let's take a look at the Fully Diminished 7th chord. Typically this is notated (using C again as an example) either as: C°7, or Cdim7.

There's a few things to note here! First of all, we're looking at a double flatted 7th here... is this a new interval? Well, not really. It sounds just the same as a Major 6th.

It's a little odd, but western music theory likes to do things like this to keep certain systems intact.

The fully Diminished 7th chord

Guitar fretboard diagram showing B flat7, B flat5, B flat3, and a red circle with the number 1 on the right side of the strings.

It might seem less strange if you consider that we also have two names for accidentals (sharp/flat notes). G# and Ab, for example.

Moving on, it's very interesting to note that this chord is nothing but Minor 3rds stacked on top of each other. If we played an octave of the root on top of this, that would be another Minor 3rd from the bb7 to the octave. Each note is the same distance apart from the next, and this symmetry leads to some cool possibilities, which we'll look at later in this lesson.

Let's look at some more useful ways to play the chord than the above. Again, we have an E, A, and D string root option here.

Guitar tab sheet showing chords with fret numbers and notes, including B7, B3, D7, F5, Gb7, and B5.

As we no longer have the jazzy Minor 7th interval softening up the chord, it's sounding much more tense and unsettling.

You might be wondering if this chord is diatonic to a scale. The answer is yes! It's found when building a chord from the 7th note of the Harmonic Minor Scale. But that's not a particularly helpful bit of knowledge for anyone that doesn't already grasp why the Harmonic Minor Scale exists.

So what can we do with this crazy chord? To help make sense of this chord's sound, let's check out how it compares to the Dominant 7th.

Below, we can compare a Dominant 7th shape to a Diminished 7th one. Although technically the intervals it's built from have all changed, really, it's more like the root note moved up a fret. If we compare, for example, a G7, and a G#dim7, they actually only differ by one note.

G7: G-B-D-F

G#dim7: G#-B-D-F

Guitar chord diagram showing a diminished seventh chord on the first and fifth strings, with finger positions indicated.

Now we can see that the Dom7 and Dim7 are actually quite similar chords. (And so are the names! Don't get them mixed up.)

I'm pointing all this out because in fact the Fully Diminished 7th chord is often used in similar situations to the Dominant 7th. We can substitute it in to spots where a V7 would function.

Let's try it now. Try playing this cadence: G7 - C.

Then, try subbing in the Diminished 7th with: G#dim7 - C.

It sounds okay, right? Maybe a little more dissonant than you're used to, but not terrible. We can do better, though!

Now let's see how the symmetry of the chord comes into play. Below, we have the G#dim7 chord repeatedly being shifted up three frets. Take a look at the notes! Although the order changes, we end up with the same 4 notes every time.

This opens up some really neat ideas for improvisation and songwriting, but we won't get carried away for now.

String of musical notes on a guitar fretboard with chord diagram, indicating the positions for playing a song.

So, instead of jumping all the way from G#dim7 to C, we're going to use Bdim7 instead! It has all the same notes, so it will still serve the same function.

The difference? The root note on B serves as a leading tone back up to the C root which enhances the feeling of resolution.

Here's one way I like to voice this cadence.

That doesn't sound half bad, right? Now we've found a way to incorporate the tension of this chord. We're not diatonic anymore, but we're just barely outside the scale.

Most times a chord progression goes non-diatonic, you will find that there's a strong theoretical backing behind why, if you can understand how all the pieces fit together.

Sheet music with musical notes and guitar tab notations.

There's so much we can do with Diminished Chords, but I hope this gave you something interesting to play with for now.

Remembering the link between Dim7 and Dom7 chords goes a long way towards uncovering their use cases.

If you'd like to see another common use case, let's talk about Passing Chords!