Really, there's no such thing as a “blues” chord. A chord is a chord - Any chord can be used in a blues progression or song. The only name a chord have is its actual name, like: C, C7, Dm, Fmaj7 etc...

A chord is three or more notes sounded together. It's that simple!. A chord can be as simple as a three note triad, all the way up to a fancy jazz chord like G13+9.

There is, such a thing as a “blues” chord progression. But not just any progression is “Blues” progression. For a progression to be a blues progression, specific chords or their direct substitutes must appear at particular spots in the progression. We call this post chords.

The 12-bar blues is one of the most popular chord progressions in popular music, including the blues. The blues progression has a distinctive form in lyrics and phrase and chord structure and duration. It is, at its most basic, based on the I-IV-V chords of a key.

The blues can be played in any key. Mastery of the blues and rhythm changes are "critical elements for building a jazz repertoire".

Here is a 12 bar blues chord progression in the key of C major.

The C, F and G chords are the I, IV and V chords in the key of C major. Here are all the chords, as triads for the key of C major: C, Dm, Em, F, G, Am, and B°

The V chord, the G can commonly be a 4-part 7th chord. Sometimes called a dominant seventh. In the key of C major the V chord can be a G7 chord.

* Post Chords - Measures one, five, seven, nine and eleven are critical measures where the I, IV and V chords MUST appear or their direct substitutions for a progression to remain a blues progression.

We can call these chords and the positions that they must fall in, post chords.

The most common form of a blues chord progression is twelve measures in length containing three, four measure sections:

• 4 measures of the I chord. ( measures 1, 2, 3 & 4 )
• 2 measures of the IV chord ( measures 5 & 6 )
• 2 measures of the I chord ( measures 7 & 8 ).
• 2 measures of the V chord( measures 9 & 10 )
• 2 measures of the I chord( measures 11 & 12 )

Totaling 12 measures

While other measure lengths are possible, such as eight and sixteen measures, the twelve measure form is the most common.

The simplest blues would actually be the I chord for the twelve measures. Or, an indeterminate number of measures, as the blues where first sung by the field slaves of the southern states in the USA.

Two blues progressions lessons from my book, A Guide to Blues Progressions for Ukulele from A to Z.

• Blues Progression - Major “Quick Four” Progression
• Blues Progression - Example J, Diminished Seventh Passing Chord