You've probably heard someone say it before, "that's just a straight 12 bar blues" or something to that extent.
What exactly are they talking about when they say 12 bar blues?
How do you know what chords to play?
How do you know when to switch chords?
I'm going to answer all three of those questions in this article. After reading this you should be able to go grab your guitar and start picking out some 12 bar blues riffs in different keys that you're familiar with.
Picking the Right Notes
Understanding the 12 bar blues isn't difficult, but first you must understand a concept known as I-IV-V (one-four-five).
These numbers (or roman numerals) stand for the first, fourth and fifth notes taken from a given scale.
Example: If we're talking about the A major scale then we've got
A B C# D - E - F# - G# - A
Our one is going to be an A note, our four is going to be a D note and our Five is going to be an E note.
If we consider those notes as chords (or power chords more often then not when playing the blues) then we get the chords we need to plugin to our 12 bar blues pattern.
The 12 Bar Blues Pattern
So like the name suggests the 12 Bar blues pattern consists of 12 bars. For our example we'll assume that each bar contains 4 beats.
The pattern looks like this: 1 1 1 1 4 4 1 1 5 4 1 5
What do these numbers stand for? If you guessed the notes/chords we determined above you'd be right.
We play a particular note or chord for each one of the 12 bars in the pattern starting with the one chord, followed by the four chord, then the one chord again then to the five etc.
That's it, you now understand the basics of the 12 bar blues pattern.
Of course in order to play it in different keys you need to understand what notes are in each particular scale and then be able to pick out the one the four and the five, but the pattern will always stay the same.
So go grab your guitar and give it a shot with this A major 12 bar blues progression.