Over the years I’ve found that while most guitarists have an easy time learning to comp and solo over the 12-bar blues, many people struggle when it comes time to expanding this well-known progression beyond the standard three chords. While there are many ways to apply chord substitutions to the 12-bar blues, I find that by applying one sub at a time, and keeping things simple, it’s easier to get these new chords under our fingers and in our ears.

One of the first subs I teach within the context of a 12-bar blues is the #IV diminished 7th chord. This chord sub is commonly found in traditional blues, jazz, rock, RnB, gospel, funk and just about every other genre you can think of that borrows from or uses the 12-bar blues form within its song structure. Alright, enough talking, let’s dive in and see how this chord sounds when we add it to a 12-bar blues in the key of A.

Before we add the #IV diminished 7th chord to our blues, let’s just take a look at the first four bars of your typical 12-bar blues in the key of A major.

Example 1.

Bars 1-4 A Blues

Basic Blues Subs – Example 1

Pretty basic right, so let’s spice it up by adding the #IV diminished 7th chord between the IV chord, D7, and the I chord, A7. In order to allow for a smooth transition in the bass line, try using an A7/E chord in bar 3. This gives you a nice D-D#-E melody line in the bass, which is typical of what bass players would play over these three chords.

Example 2.

Bars 1-4 With D#dim7 Added

Basic Blues Subs – Example 2

Now that we’ve learned to use the #IV diminished 7th chord in the first four bars, let’s apply it to the middle four bars of an A blues. Notice that harmonically this new chord lines up right where it did in the first four bars, between the D7 chord and the A7 chord. If you are assuming that you can now use the #IV diminished 7th chord to connect any IV and I chord, then you’re right. There are other places we can put this chord, but for now feel free and try it out on other tunes you’re working on that have a IV chord moving to a I chord.

Example 3.

Bars 5-8 With D#dim7 Added

Basic Blues Subs – Example 3

Last but not least, we’ll add this new chord into the final four bars of the A blues. By now you’ve gotten the hang of it and you’ve probably figured out where it’ll line up in the progression, but just in case here it is for good reference.

Example 4.

Bars 9-12 With D#dim7 Added

Basic Blues Subs – Example 4

Since the diminished 7th chord may be new to some or most of us, I’ve included four standard voicings for this chord for easy reference.

Example 5.

Four D#dim7 Chord Voicings

Basic Blues Subs – Example 5

Now that you’ve worked out adding the #IV diminished 7th chord to all three sections of an A blues, try and add it to other songs you’re working on. You might be surprised to find that by adding one little diminished chord to a tune, you can create many added levels of interest in your playing.