Although not a Structure in the same sense as the preceeding
examples - This Three Chord Trick of Seventh chords is useful in understanding
the complex make up of the Blues style.
Each of these chords contains four different notes so when we analyze all the notes we don't end up with a seven note scale as we did in the previous examples but we do end up with the selection of notes we need to play Blues.
It is the way these notes are put together as melodies that makes the style happen.
See my tutorial on the Major Blues Style for more information on this subject. See also my videos on The Blues Scale
For now I'd say that you can't learn to play Blues music properly by using just one scale.
This Three Chord Trick demonstrates this (you can't fit all these notes into one scale).
You can certainly play blues chord sequences without using 7th chords but this structure gives the full complexity of the style.
This structure can also be used in some non-blues styles such as soul and funk - check out James Brown's ' I Feel Good ' for an example.
Work out all the notes that are contained in these three chords and learn the A Minor pentatonic scale and the A Major pentatonic scale.