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" :-)