Pentatonic scales and chords
The pentatonic scale has many variants and a long history. There are lots of web sites, books, and learned papers that document its use across time and cultures. Here I just want to try to show the essence of what makes the pentatonic scale, as it is generally defined and used in most western music, so important. The pentatonic scale we tend to learn first is the minor pentatonic. The pentatonic minor scale is just the 1st, 3rd, 4th, 5th and 7th of the minor scale. There are five patterns (aka positions) for this pentatonic scales. Like any other minor scale, it can be played over the minor chord and its relative major chord. As a result, each of the five pentatonic scale patterns is associated with a minor and a major chord shape, which are the CAGED chord shapes.
This shows the five pentatonic patterns and their associated CAGED minor chords. As well as remembering the association between the pentatonic pattern and the chord shape, it is useful to remember the root note for each of the chords.
This shows the same five pentatonic patterns and their associated CAGED major chords. Note that the relative major of G minor is A#. It is always easy to find the relative major of a minor as it is will be 3 semitones (frets) higher. (Step back one fret and your at the Major 7th, then two frets and its the 6th).
Mashing pentatonic scales together
One of the key ingredients of the blues sound is the pushing of a major key into a minor key or visa versa. You can do this in lots of ways. One very useful way is to merge/mash together the major and minor pentatonic scales. So taking Gmajor and Gmin we can merge these to get a scale that has an interesting sound that includes a nice 4 note chromatic run. A second 4 note run can be created by adding in the so called 'blues note'... a flat 5. To create the scale you just take a major pentatonic pattern and merge it with the preceeding pentatonic pattern.
This shows the five pentatonic maj-min patterns:
Pentatonic patterns and Modal patterns
To understand this section you need to know a bit about modes. This bit is here as it completes the circle of how CAGED chords, pentatonics and modes are all related. I have never seen this made sufficiently clear in any book or web site that I have come across. I suppose to some it may be obvious... it certainly wasn't to me!
There are seven modes, one for each note of the Major scale. However, the scale patterns for the Phygian and Lydian are the same, apart from one note. The same is true of the Ionian and the Locrian. So we only really have 5 distinct scale patterns which are just extensions of the 5 pentatonic patterns. Yes, the penatonic patterns are really the pentatonic notes selected from the modal pattern ... but we are looking at this from the point of view of pentatonics and the CAGED chords.
So the following illustrates the mapping between modal scale patterns and the pentatonic scale patterns. So 'P1' is Minor Pentatonic position one, etc. The blue notes are the penatonic pattern. This example is based on the scale of C Major but obviously it is a moveable feast: