When we studied 7th chords we saw that we can move the octave of a major chord back one or two semitones to get a major or a dominant seventh. What would happen if we moved it back another semitone? Would we get a 6th chord? Yes, but In some cases we would get a diminished 7th interval, it depends on the scale that generates the chord.

This particular chord has a minor third, a diminished fifth and a diminished seventh and strangely enough is called a Diminished chord. It's a really peculiar chord because the interval between each note is always a minor third, one and a half semitones and so every note can be considered the root and we get 4 different chords with one position.

Though this chord is really a minor, flat fifth, minor seventh chord (which we didn't study already but is also called a half-diminished chord) where we move back the seventh another semitone, a much more simple way to find it is to take a seventh chord and raise the root by a half step.

So let's take a simple D7 chord and move the root (open D string) up one fret to D# and now we got a D# Diminished chord (or D°).

From an harmonic point of view, the two chords share three notes out of four and so the diminished chord is often used a substitution of the dominant seventh to add more tension or resolve to a new key.

We said that every note in the chord is a root so we can use the same position for A°, C° and F#° too.

It's a simple and easy to play shape with no open strings so we can easily move it up the fretboard in three fret increments to play any of the four chords in a different part of the neck, with a different 'leading' note and a different root.

There are just 3 dimished chords with four inversions but every inversion starts on a different root or you can locate any note you like in the chord and that will be the root... Probably easier to try it than to explain it.

Though this is the easiest shape to remember and to play, there are obviously many other fingerings we can use but we can keep things simple by altering the other two main open shapes: A and E.

Let's start with an A7 and move the root up one fret: instant A#°!

To find a movable shape with no open strings we slide everything up one fret and add a finger on the first fret of the 3rd string to get a B°: we can use this everywhere on the neck as long as we remember not to play the first and sixth strings.

Let's repeat the same process to find dimished chords with the root on the sixth string: start with an open E7 shape and move the root up one fret to get an F diminished. We can't play the first string anymore since E is no longer part of the new chord.

We mentioned Half Diminished chords (or minor 7th flat 5 chords or Ø) and though they're a lot less common than diminished chords, at least in Pop and Rock music, it may be useful to know them. The difference from a diminished chord is the seventh that is just minor (so up one fret) and the difference from a minor seventh chord is the flat fifth (one fret down).

Let's see all three chords starting from the D shape so you can see the note movement in both cases.

In the D#° chord we move the diminished seventh up one fret to a minor seventh and in the D#-7 we move the fifth back one fret to a flat fifth.

In the A and E shapes we'll just see how to get a Half Diminished chord from the diminished chord because we haven't seen any barre chord yet.

From B diminished we raise the diminished seventh on the 3rd string to a minor seventh to get this easy and nice sounding shape that we will probably use a lot when we need a half diminished chord.

Same thing with the E shape, this time the diminished seventh is on the fourth string.

There's an additional way to find half diminished chords, starting from Major Seventh chords and raising the root up one fret, quite like what we did for Diminished chords but this time the starting seventh is major so in the resulting chord it will be minor.

Let's see how we can do it in the three basic open shapes. We can move all the new shapes around if we remember to play just the fretted notes.

Remember that half diminished chords work just for that one root, they're not symmetrical like diminished chords.

Now that we've seen these quite peculiar chords, let's see if we can find more cool open chords that we can play easily...