It takes quite a long time for us guitarists to see chords for what they really are: a batch of specific notes chosen from the scale. We tend to see chords as compact groupings of notes in familiar patterns but that's not really the full picture. Because chords are just a selection of notes, and notes repeat themselves all over the fretboard, then it follows that chords also repeat themselves all over the fretboard. They do that in a very specific way, and that's what this lesson is all about.
Lets look at a C major chord. C is always a good example because the key of C uses all natural notes, so there are no pesky # or b signs to muddle the brain.
The C chord is the result of selecting the 1st, 3rd and 5th notes of the C scale. The scale is C D E F G A B, so those three notes are C, E and G. Play them together, and you've played a C major chord.
If you mark all the C, E and G notes on a guitar fretboard, this is what you get:

... which looks like this as dots.

This is the pattern made by all the chord tones of C. This pattern is referred to as the
CAGED pattern because it consists of all the open chord shapes -- the
C shape, the
A shape, the
G shape, the
E shape and the
D shape -- strung end to end. Here they are below. I used the word "form" instead of shape. Same thing, in this case. You should be able to see each of these as open chords moved up the fretboard and barred. Even if you never use some of these AS chords, it's important that you know where those moveable shapes are for whatever chord.

They then start repeating past the 12th fret, one octave above:

Here they are again:

From left to right, you can see the faint green square contains a good old C chord; the lilac square contains the barred A shaped version; the blue square is the G shaped C chord, not one you'd use very often; the pink square contains the barred E form version of C major; the light grey box contains the D shaped version, and then we're back to a C shape and octave up. Notice how the boxes overlap, how all the shapes share notes.
THAT's a C chord. That whole fretboard, as depicted above is a C major chord, or I guess I should say a 'potential' C chord. It's also potential melody and harmony, since both use the same notes as the chord.
And how is this helpful, you may ask? Well, if you want to have complete freedom on the guitar, you have to be able to use every part of the fretboard; there should be no grey areas, no off-limit places, no scary bits. When I started playing, anything past the first 4 or 5 frets was no-go-zone. Way too scary to venture up there ... I marvelled at anyone who could go playing way up there without a net below. What I didn't realize was that they were not measuring everything from the nut up, as I was. For me, way back then, the nut was my zero mark ... my point of reference. I was counting up from there to keep track of what I was playing, to remember where notes were. It was when I decided to let music herself show me the way, not that physical place where the strings ended, that all of a sudden I began to see the light.
The movie shows me doodling in C. I first play all those CAGED pattern notes. These are all 1-3-5's of a C chord, and it sounds like an opera singer warming up. If you want to practice this (which would be a GREAT thing to practice), just play all the notes in the graphics above.
I then play a few double stops (two notes played together), both notes coming from that same template. You can see how easy it is to create harmony lines when you know that pattern backwards and forwards, as I do. Any combination of notes chosen from that pattern, played in any order, will be 'right' for C.
The last bit of the movie is me playing a riffy, bluesy kind of thing, off the top of my head, in C. You'll just have to take my word for it that I'm following that same template when I play this. You can see and hear that I'm playing a lot more than just those CAGED notes; that's because I also know all the in between notes, but it's those CAGED notes that are the launch and resolve notes of my riffing. They're home. I just have a lot of ways of leaving and returning home ... I know all the back streets and alley ways that connect up the main roads.
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