I know that CAGED is mainly a way to figure out how to play the same chord in multiple variations throughout the neck. So you'd take the chord C for example, and you can play it using C-shape, A-shape, G-shape, E-shape, D-shape.
But I'm wondering if CAGED is also a good indicator of the most popular keys to practice on the guitar. Do guitar players usually gravitate towards the keys of C,A,G,E,D or is there no correlation?
The 'caged' system reflects the fact that there are several open chord shapes available on guitar, which can be ( and are!) transferrable up the neck, with the addition of a barre, thus producing the same chord shape, but in different keys. Or - one can play certain chords in five different shapes in different positions on the fretboard.
Because they start out as open chord shapes, most beginner guitarists will learn them as such fairly soon in their progress. Some will never or rarely venture past that stage, using a capo instead. Others will be well aware of the shapes, and use them to produce chords in all of the 12 keys.
They are undoubtedly the most used major shapes on guitar - although there doesn't seem to be an equivalent for minors. However, there is no reason to presume that those five shapes indicate that they reflect any compunction to 'practise in those keys'.
In fact, considering all five chords, A D and E are a 'family', as is G C and D, and D G and A (Family = I IV and V) so practising in key C, or key E will inevitably involve other shapes.
To answer your question, no the keys of CAGED aren’t really of any significance, just the shapes of those chords in their open positions.
I didn’t learn using the CAGED system but I see its value. It isn’t about practicing particular keys, but understanding how those chord shapes relate and connect no matter what key you’re in. In addition to them being chords, the shapes can serve as a framework for arpeggios, which you can then extend into additional scale tones, chromatics, chord inversions, what-have-you. If you learn all these shapes, how each relates to the next and where the roots are, you can play all up and down the neck, focusing in on each CAGED position and/or the transitions in between, regardless of key.
All the 'CAGED' chords are open chords: on a guitar with standard tuning all these chords use some open strings. They allow the player to get a full sound without using a barre, like you would need for, say, Eb, F#, G# chords etc, so they are easier to play, and therefore guitar players gravitate to the CAGED chords. Once a guitarist can visualise the fingering for these chords they are in a position to use them in different positions on the neck and play, say, an E chord with D fingering, or a G chord with A fingering and even, if they put their mind to it, a Bb chord with D fingering.
There are also corresponding CAGED scale fingerings that a CAGED-aware guitarist can use all over the neck.
The answer to your question: at first, and sometimes forever, guitarists gravitate to the CAGED keys because they are easier to play on the guitar. It must be noted that there is a subset of guitarists who stick to the inaptly-named 'power chord', which can be played with two fingers on two strings and moved all over the neck.
The 'common fact' here is that C, A, G, E, and D are the open chord shapes in standard tuning.
This fact is part of the reason why the keys C, A, G, E, and D may be easier to play in.
That same fact is part of the reason why the CAGED system is called the CAGED system (plus the fact that the chord shapes visually interlock in that order).
But the logic of the CAGED system itself doesn't really have any bearing on what keys are easy to play in. In fact the system encourages movement up and down the neck, while if you were wanting to get maximum leverage with minimum effort by using the open chord shapes, you'd be doing the opposite of that and playing those shapes open.
The CAGED system relates the open string major chord forms to movable forms. There is more to the system than just these 5 chords. Each has a corresponding mode (version of the major scale) that the chord fits easily into making it fairly easy to connect the scales up the neck to the chord form. Also, these chords are connected, for example The bar of the A-form usually made with the 3rd finger is the bar of the G form made using the 1st finger. The D-form overlaps the C-form. With these connection one could, for example, play a one chord Vamp in A walking all the way up the neck and back. So you see that the CAGED illustrates how the geometry of the chords and modes is laied out on the neck for a single key. All keys are important but some more common on guitar. And those might just be keys with an abundance of open chord forms in them! However I wouldn't say that the keys of C, A, G, E, and D are the most common or include all the most common keys. F is an important one and there are some fairly famous classical pieces in D min (relative minor to F maj) so I'd say that is an important key. The value of understanding the CAGED system is that once you can move the chord forms around the neck changing key is just a matter of shifting to the correct fret. In fact, once you really understand and master the guitar you can transpose while sight reading by simply moving the hand to the correct location. Of course this requires not looking at your hand, which many guitarists are unable to do.
The short answer to your question is no, CAGED does not indicate the keys to practice. Some of us play in Bb all day to make horn players happy. But we still use the CAGED to get around.
It is my understanding that the CAGED system on guitar was developed to help a player be able to play in any Major key on the guitar neck by showing us how the five basic open chord shapes can be movable up and down the neck by adding the Barre finger into the chord shape. This appears as a short cut to using the full capabilities of the neck and all the keys instead of the idea that these are the most common keys you'll need to practice in order to get good. It should be emphasized that when you are learning the CAGED system, you should be moving those chords up and down the neck between the first and twelfth fret, and doing so would mean that you're practicing in every major key.
Sort of.
CGDAE makes more musical sense, but you can't say it so it isn't a cute mneumonic.
Open strings are EADGBE ...it's inconvenient to play a key that puts and accidental on any of the open strings. Let's use that criteria for: a good indicator of the most popular keys. But we need to use sensible music theory instead of a mneumonic to get the answer. Assess key signatures in relation to the open strings.
Go the way of the flats first: Bb stop! You hit one on the first key signature with a flat. Keys with flats are inconvenient on guitar standard tuning.
Next, sharps. F#, C#, G# stop! Up to two sharps is OK. After that you can't use the open strings for key signatures with 3 or more sharps.
Back to CGDAE disorganized as CAGED. Start with C using zero sharps and flats then go up (in fifths, hence my complaint about the order of letters in CAGED) and D is the key signature with 2 sharps. So, C, G, and D use all the open strings which makes them pretty convenient keys to play on standard tuning.
C-G-D is what you are left with from the word "caged."
Or, just CGD and not A or E.
Not much of a mneumonic, but you don't need a mneumonic with a sound grasp of the core theory of key signatures and musical spellings in perfect fifths.
You might ask further: why not FCGDA, isn't F just as inconvenient as A in that both are only one accidental past the open strings? The trouble with F or any of the flat key signatures is that you need to lower the B to Bb. How do you lower an open B string? Of course you can't. You have to skip using the open B string and fret it somewhere else. By comparison adding sharp keys to CGD like A and E involves just fretting one of the open strings on the first fret which isn't as convenient as playing all open strings, but a lot easier than dealing with flats.
Maybe you can fudge things a bit and use lowercase to indicate minor keys for a and e minor. Those key signatures are of course zero sharps and flats and one sharp respectively. CGDae or camelcase CaGeD! Actually, that isn't half bad as the relative major/minor keys are paired up!
CaGeD, but pronounced with soft A and hard G, like "kah-ghed" :-)
