Blues Guitar Institute

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Play 12 Bar Blues in Any Key with These 3 Easy Steps

Lesson ID: TB428

Ever notice how some chord progressions feel the same, even when they use completely different chords? Take these two for example:

C – G – Am – F


E♭ – B♭ – Cm – A♭

If you play them, you might hear that they have a lot in common.

Different chords, but they sound similar. Want to know the reason behind it? It’s all about the job each chord does in the progression.

There’s a tool that lets us talk about chords and their jobs without being tied down to a specific key. We can use this tool to find that both sets of chords we just looked at follow the same pattern:

I – V – vi – IV

This tool is called Roman Numeral Analysis. It’s handy for understanding how chord progressions work. Plus it helps you communicate with other musicians about chord progressions. Think of it as a shorthand for progressions that’s completely key independent.

But one of the most practical uses of this tool?

Changing keys.

In this lesson, we’ll use Roman Numerals to change the key of a basic 12 bar blues progression. It takes three easy steps.


Step One: Assign a Roman Numeral to Each Chord in a Key

Before we dig in with a practical example, you’ll get the most out of this lesson if you already:

  1. know the note names on the fretboard and
  2. know the chords in each key.

If you don’t know the chords that belong to every key, start by memorizing the most common guitar keys – E A D G C.

If you’d rather not memorize, I teach a quick hack to learning this on the Fretboard Roadmap inside myBGI.

Now, let’s start by writing the chords from the Key of E Major.


Next, replace each chord in the sequence with a Roman Numeral. Start with I and increment by one as you move across the sequence. You’ll get this:



But did you notice that some of the numerals are uppercase and others lower? And there’s a weird symbol on the last chord?

In Roman Numeral Analysis, major chords are usually written uppercase and minor chords are lowercase. This is a quick way to see which chords are major and which are minor in a progression. The 7th chord in the key is a diminished chord which is different than major and minor. So it gets a special symbol (°) all its own.

This first step isn’t difficult, but it has a huge hidden benefit.

Think of each Roman Numeral as a label for the job – or function – of each chord within the key.

For example, the vi chord, C#m will have the same job in the Key of E as F#m does in the Key of A.

Begin thinking of chords as the job they perform in the key. This will help you quickly identify chords and entire progressions when you hear them.

Let’s see this in action with one of the most common chord progressions: twelve bar blues.

Step Two: Convert the 12 Bar Blues Progression to Roman Numerals

Let’s analyze the 12 Bar Blues Progression in E with roman numerals. Start with the progression like this:

12 Bar Blues Progression in E


Now replace each chord with it’s roman numeral like this:

12 Bar Blues Progression in E


Notice that we only used the I IV and V chords in the progression. That is common in 12 Bar Blues. You’ll find plenty of variations in the Blues, but the I IV and V chords show up a lot.

Know them!

But go beyond knowing the I IV and V of each key, know how the IV and V sound within the key. When you do this, you’re learning the job of the chord. You’re learning its function which makes it useful far beyond 12 Bar Blues.

Don’t Limit the Progression to Playing the Chord

We’ve talked a lot about chords. Twelve Bar Blues is a “chord” progression after all. But it’s actually broader than that.

In some styles, the Roman Numerals strictly represent a chord. But in the blues, each numeral can represent many things like:

  • Shuffle Riffs
  • Boogie Patterns
  • Slide based riffs

For example, when we play the standard shuffle pattern we can play it along with the progression. But instead of strumming an E, A and B chord, we play the riff in E then A and B.

Let’s see the power of Roman Numerals in action by changing the key of the twelve bar blues progression.

Step Three: Change the Key Using the Roman Numerals

With practice, changing the key using this tool becomes second nature. Here’s how it works.

First, remember the pattern:


Let’s say we want to play this in the Key of A Major. We’ll need the I IV and V chords from the Key of A: A D and E.

Now let’s plug them into the chord chart above:


Let’s try a key that’s used a bit less often, B♭:


Try playing each of these on your guitar. Notice how the D in the first progression has the same job as the E♭ in second. They are both IV chords in the progression.

Here’s the win:

It’s more efficient to memorize the Roman Numeral pattern rather than memorizing the pattern in all 12 keys.

And, as you’ll see in future lessons, the Roman Numeral system is very expandable.

The Most Helpful Thing About Using This System

We’ve looked at a practical example of how you can use the Roman Numeral system in your playing. But remember this:

Roman Numeral Analysis is a tool.

It’s a tool that makes learning a progression portable to any key. And the big bonus is that when you truly learn this tool, you begin hearing the jobs the chords perform.

This will help you recognize the jobs certain chords play within a song which helps you learn by ear faster.

Don’t get me wrong – everything doesn’t need to be faster on your musical journey. But, wouldn’t it be cool to immediately recognize entire progressions and focus on other things?

Things like making the chords musical and expressing yourself on the guitar.

That’s the goal and I know using the Roman Numeral tool can help you get there.

When you are ready, there are two ways I can help you:

Back Porch Blues Course:  A proven system to fingerpicking the blues.  This step-by-step course guides you through building fundamental fingerpicking skills.  Plus, you’ll learn three levels of a delta blues style performance study to put your new skills into action.

Become a myBGI Member: Membership comes with access to Back Porch Blues plus over 70 step-by-step courses.  Get proven results with one of myBGI’s structured Roadmaps.

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