a type of chord that includes the 7th scale degree (that is, the 7th note of the scale). There are different types of 7th chords such as major 7ths, dominant 7ths, minor 7ths, half diminished 7ths, and fully diminished 7ths. These chords are similar with slight changes, but are all centered around the same key center. Dominant 7th chords are generally used throughout a blues progression. The addition of dominant 7th chords as well as the inclusion of other types of 7th chords (i.e. minor and diminished 7ths) are often used just before a change, and more changes can be added. A more complicated example might look like this, where "7" indicates a seventh chord: {|class="wikitable" style="text-align:center; width:130px;" |width=25%|I |width=25%|IV |width=25%|I |width=25%|I7 |- |width=25%|IV |width=25%|IV7 |width=25%|I |width=25%|I7 |- |width=25%|V |width=25%|IV |width=25%|I |width=25%|V7 |- |} Bebop blues This progression is similar to Charlie Parker's "Now's the Time", "Billie's Bounce", Sonny Rollins's "Tenor Madness", and many other bop tunes. Peter Spitzer describes it as "a bop soloist's cliche to arpeggiate this chord [A79 (V/ii = VI79)] from the 3 up to the 9." {|class="wikitable" style="text-align:center; width:250px;" |width=25%|I7 |width=25%|IV7 |width=25%|I7 |width=25%|I7 |- |width=25%|IV7 I7 |width=25%|IV7 |width=25%|I7 |width=25%|V/ii9 |- |width=25%|ii7 |width=25%|V7 |width=25%|I7 V/ii9 |width=25%|ii7 V7 |- |} Minor blues There are also minor twelve-bar blues, such as John Coltrane's "Equinox" and "Mr. P.C.". The chord on the fifth scale degree may be major (V7) or minor (v7). Major and minor can also be mixed together, a signature characteristic of the music of Charles Brown. {|class="wikitable" style="text-align:center; width:130px;" |width=25%|i7 |width=25%|i7 |width=25%|i7 |width=25%|i7 |- |width=25%|iv7 |width=25%|iv7 |width=25%|i7 |width=25%|i7 |- |width=25%|VI7 |width=25%|V7 |width=25%|i7 |width=25%|i7 |- |} Other variations "W.C. Handy codified this blues form to help musicians communicate chord changes." Many variations are possible. The length of sections may be varied to create eight-bar blues or sixteen-bar blues. Melodic line As the chords of a 12 bar blues follow a form, so does the melodic line. The melodic line might just be the melody of the piece or it might also include lyrics. The melody and lyrics frequently follow an AA'B form, meaning one phrase is played then repeated (perhaps with a slight alteration), then something new is played. This pattern is frequently used in the blues and in musical genres that have their roots in the blues. See also Eight-bar blues Sixteen-bar blues Bird changes References Sources Chord progressions Song forms Jazz genres Blues music genres