The main chord progressions in blues explained

I try to practice like a well rounded regiment of things where I can kind of do whatever I wanna do and I also have to practice the actual songs to keep that under my fingers as well.” B. B. King

A blues chord progression is series of chords with a specific tonality, or sound, relative to the tonic chord. When all of the chords in a progression belong to the same major or minor key, the progression is considered to be diatonic in nature. If one or more chords fall outside the key, then the progression is considered to be non-diatonic.

Diatonic and non-diatonic chord progressions

Diatonic progressions are prevalent in popular music, and pop songs that do employ non-diatonic progressions usually consist of only one or two chords that fall outside the key. The best genre for hearing non-diatonic progressions in action is jazz, which typically involves highly sophisticated non-diatonic chord changes. In this book, we’ll focus on both diatonic and nondiatonic chord progressions, with an emphasis on the former.

If we take the C major scale and build diatonic triads on top of each scale degree, we would end up with the following chords:

Notice that none of the triads contains a sharp or flat—they’re all “natural” notes—which is an indication that all of the chords are relative to the key of C major (or A minor).

If you refer back to our table containing the 12 major scales, you can see how some triads must be altered (relative to their parallel major scale) to accommodate the “new” key—in this case, C major. For example, the D major scale (D–E–F#–G–A–B–C#) contains a major 3rd, F#, but the ii chord in C major (Dm) is minor in quality.

The solution is to lower the 3rd from F# to F (one half step) to accommodate the C major key center. The same goes for the iii chord: the 3rd of the E major scale (E–F#–G#–A–B–C#–D#) is G#, which must be lowered one half step (to G) to make it minor in quality and diatonic to C major.

Some of the triads, like F and G major, require no adjustments at all.

The structure of blues chord progressions

This is type of analysis (i.e., comparing each triad to its parallel major scale) can be a bit confusing. What’s important to know is that, regardless of the key, the chord (triad) qualities in a diatonic progression always remain the same: I–ii–iii–IV–V–vi–viidim (major–minor–minor– major–major–minor–diminished). We’re simply taking the notes of a major (or minor) scale and stacking 3rds—that is, every other note of the scale—on top of them. The result is the seven triads indicated above.

The Roman numerals indicate the scale degree relative to the tonic, as well as whether the triad is major (uppercase) or minor (lowercase). (Diminished triads are also represented by a lowercase Roman numeral, in addition to the abbreviation “dim” or a small, circular symbol.) The Roman numeral system is extremely helpful in regard to transposing progressions to other keys—as long as you have a firm grasp of the 12 major keys!

The same concept applies to diatonic triads in minor keys. Here are the seven triads that are built from the A minor scale:

If you look closely, you’ll notice that the chords in A minor are exactly the same as the chords in C major, only in a different order: i–iidim–III–iv–v–VI–VII (Am–Bdim–C–Dm–Em–F–G). Despite the different sequence, three of the triads are minor, three are major, and one is diminished—just like the triads of the C major scale! (Note: You will sometimes see the minor scale Roman numerals written to reflect the parallel major key rather than the relative key. In the case of A minor, the Roman-numerals would reflect the A major scale [A–B–C#–D–E–F#–G#]: i– iidim–bIII–iv–v–bVI–bVII.)

The same concept applies to seventh chords. Here are the seven diatonic seventh chords that can be built from the notes of the C major scale:

Again, the chords in both keys are exactly the same, only the sequence is different.

By stacking one more 3rd on top of the triads of the two scales, we get two major seventh chords (Cmaj7 and Fmaj7), three minor seventh chords (Dm7, Em7, and Am7), one dominant seventh chord (G7), and one minor seventh flat-five chord (Bm7b5). The sequences and chord qualities remain constant in any major or minor key. Before we talk about non-diatonic progressions, let’s spend some time discussing another crucial component of modern lead guitar—modes. In addition to the actual modes themselves, we’ll talk about progressions that can be built from these scales.