Understanding Blues Forms and Common Substitutions

In this lesson, we’re going to examine a couple of different blues forms, specifically the 12 bar, 8 bar, and 16 bar blues. Additionally, we’ll go over a few different approaches to playing through the form and knowing when it would be appropriate to substitute chords or when to adhere to the traditional changes.

Here is a diagram outlining the standard 12 bar form:

12 Bar Blues

The roman numerals I, IV, and V refer to the “one,” “four,” and “five,” chords in the progression. If you’re new to music theory, think of playing a C major scale and attributing a number to each note of the scale. C=I, D=ii, E=iii, F=IV, G=V, A=vi, B=vii (lower case indicates minor chord). If we’re playing a blues in the key of C, the I chord is C, the IV chord is F, and the V chord is G.

Some common substitutions in the form include a “quick IV,” where the second bar of I is changed to a bar of IV. Another common change is a “ii-V turnaround” which applies to bars 9 and 10. If we were in the key of C, the changes would go D to G instead of G to F.

16 bar blues progressions are similar to the 12 bar blues, however the one chord is held for 8 bars instead of 4 at the beginning of the progression. Many blues songs have verses that follow the 16 bar form and then switch to a 12 bar form for the chorus or solo sections.

16 Bar Blues

An 8 bar blues typically follows this pattern:

8 Bar Blues

Think of the song “Key to the Highway” to hear this progression. A common alteration for this progression is substituting a VI chord (A in the key of C) for the IV chord in the third bar of the progression.

Now that we’ve gone over the basic forms for these chord progressions, it’s time to think about how we can approach playing through these changes. Think about who you’re playing with and whether or not the players intend to play traditional blues or jazzier blues.

The traditional blues players typically want the bass player to stay true to the form. It’s the bass player’s job to clearly outline the I, IV, and V chords and to stay with a specific bass pattern. There isn’t much room for improvisation when it comes to the chord changes because the lead instrumentalists or vocalists are expecting to hear the standard 12 bar changes; therefore, if you find yourself playing in this situation, chord substitutions usually are not welcome. Some blues standards dohave other kinds of turnarounds, such as “The Thrill Is Gone” where the turnaround is ?VI-V-I instead of V-IV-I, so it’s best to familiarize yourself with some standard tunes.

One common complaint that I hear is that bass players find it “boring” to only play over these three chords. If you find yourself getting bored, think about howyou’re playing the notes. Appreciate how a simple part can be exactly the right thing and that the other members of the band want your bass line to sound a certain way.

Many jazz players will say “let’s just jam a 12 bar blues” or they may suggest jazz standards that follow a 12 bar form (such as “All Blues” or “Blue Monk”). In this situation, you may be able to take some liberties with the chord changes by using substitutions or passing tones. With blues players, the turnaround is implied to be V-IV-I, however, my experience playing with jazzier ensembles suggests that ii-V-I is the preferred turnaround.

The best thing to do any playing situation is to listen. By paying attention to the other players, you’ll hear the chord progression that they play as well as the chord substitutions that they use. Make eye contact with the keyboard player or rhythm guitarist to see what they are doing. They will appreciate your willingness to follow along with chord substitutions and it will help you develop your ear. Be on the lookout for common changes, such as a chromatic move from the I to the VI chord (followed by a ii-V-I turnaround) or for an extended circle of fourths change: vii-iii-VI-ii-V-I.

Although there is no guaranteed way to know exactly what to play every time you get on the bandstand, remember that your ear is the best tool you have. Also, keep context in mind and feel out the other players. If you’re playing a blues gig, remember to stick to the chord progression and focus on groove. If you’re playing with jazz players who call a 12-bar, be on the lookout for other changes in the progression. The more you play with someone, the more you’ll hear certain tendencies in their playing and if you’re familiar with various blues forms, substitutions, and standard progressions, the more prepared you’ll be.

Ryan Madora is a professional bass player, author, and educator living in Nashville, TN. In addition to touring and session work, she teaches private lessons and masterclasses to students of all levels. Visit her website to learn more!

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  1. john

    So what happens if a bass player does not knw what a 1 4 5 is. or to play r 3rd and 5ths with passing tones I think this article could have been a lot better than a road map for people who already know a blues form… Especially since this is a beginner course you should have gone into more detail about how to construct the bassline over the 1 4 5 what a 145 is and so on and so forth

    • Randy

      @john- Her article was great… my question to you is are you “threatened because she is a woman, or is it because you understand so little theory yourself? Just wondering….

      • Edward

        Why even ask such question? John didn’t bring anything up about the author’s gender. However, I do think John’s criticism is valid. The article is titled “Understanding Blues Forms and Common Substitutions” and not necessarily about constructing basslines note for note, the author, I would surmise, assumes a rudimentary knowledge of chord tones (e.g. a C major chord has C,E,G)and basic diatonic harmony (e.g a D chord is minor in a C major scale).

  2. John, I appreciate your criticism but I would urge you to re-read the first few paragraphs of the column where I outline what the I, IV, and V chords are. Also, this is one column of a series on playing blues so it only focuses on one specific topic. Future columns will discuss different kinds of blues bass lines and will go more in depth regarding note choices. Thanks for reading.

  3. giuseppe

    I think that what Ryan wrote is unexceptionable.
    Nice job R!

  4. Carter Fox

    love the article, really explains info for those who want to learn it! Ryan is a great bassist, writer, and person, and this exemplifies how great she is (being able to put what you do so well into words and teach others truly shows mastery). New blues specialist teacher for Bass Bootcamp? I think so!

  5. The are tons of variations to play, even within a straight I-IV-V pattern. Most of the time when I get a nod of approval from a guitarist, it’s not from a brilliant jazz substitution – it’s from locking with the drummer and serving up rock-solid groove.

    Great article, very clearly laid out. Thanks!

  6. Lisa Mann

    When I think of 16 Bar Blues, I think of Don’t Touch Me Baby by Johnny Guitar Watson. Based on an 8 bar… The progression in 6/8
    1 / 1 / 17 / 17
    4 / 4 / 4m / 4m
    1 / 6 / 2 / 5
    1 / 4 / 1 / 5
    Is this not brought up because of it being based on the 8 bar?

  7. willy

    In the second last paragraph “chromatic move from the I to the VI chord” shouldn’t it be the IV chord instead? It seems like an obvious typo, but the author writes about the VI chord at other places so it is a little confusing.