The CAGED system is a convenient way of thinking about moveable chord shapes on guitar. On ukulele, it’s called CAGFD. Same system, just harder to say.
The basic idea is pretty simple. Take a chord in “open position” (i.e. having open strings) like C major, and slide it up the fretboard using a finger instead of the nut. Any major chord can be played with this moveable shape.
For example, to play a D major chord: start with an open position C major chord, barre your finger where the nut would be, and slide the shape up two frets. The “root note” of the chord (®) determines the name of the chord. To play an E major, slide it up two more frets so the chord’s root note is an E.
This works with the other open chord shapes too.
Some of these shapes are hard to play on some parts of the fretboard. I often leave out a duplicated note to make a shape easier to play. But it’s still useful to know these core shapes because they form the basis for other chords (shown below).
What good is this?
First and foremost, CAGFD (aka CAGED) offers a useful way to think about the universe of moveable chord shapes. It gives a name to just about every moveable chord grip; a name that is meaningful, easy to understand, and easy to explain to others. It condenses a bewildering array of chord shapes into five simple groups.
CAGFD also makes it easier to find alternate voicings for a given chord. It gives at least five possible voicings for most chords, and typically at least three of them are comfortable to play. Since CAGFD shapes always appear in order, it’s obvious where the other voicings are located. If I’m playing an A-shape chord, I know the same chord can be played in a C shape immediately below it on the fretboard, and a G shape immediately above.
This trick isn’t limited to major chords. Here’s the CAGFD system applied to minor chords.
Notice how the minor chord shapes are substantially the same as the major chord shapes, with the major third interval (3) lowered to a minor third (♭3).
Minor chord shapes are laid out in CAGFD order on the fretboard, just like major chords.
Dominant 7th chords
Dominant seventh chords (aka “seventh chords”) in open position become moveable CAGFD shapes too.
The dominant 7 chord shapes are substantially the same as the major chord shapes, with an added minor seventh interval (♭7).
Notice that the F7 chord does not actually have any open strings. Strictly speaking, that’s an E7 chord shape slid up to F.
Also notice that the D7 shape is “rootless”.
Major and minor 7th chords
Beyond the fundamental chord shapes above (major, minor, and dominant 7th), CAGFD patterns become a bit contrived. There aren’t a lot of good open position shapes for extended chords. Instead, the following chord shapes are based on a major or minor CAGFD shape, which is then altered slightly to form the extended chord.
Major 7 chords
Major seventh chords (Maj7) are major chords with an added major seventh interval (7).
Notice how similar these are to the major and dominant 7 shapes.
Minor 7 chords
Minor seventh chords (m7) are minor chords with an added minor seventh interval (♭7).
Minor 7♭5 chords
“Minor 7 flat 5” chords (m7♭5), also known as half-diminished (ø), are minor seventh chords with the fifth lowered a half-step (♭5).
These chords are rarely used outside of jazz, but they are also useful for diatonic chord studies (the VII chord in a major key or the ii chord in a natural minor key are half-diminished chords).
6th and 9th chords
Sixth and ninth chords can be substituted for major, minor, and seventh chords to add a bit of color and play with the mood. There are a variety of other options for these chord shapes, but I find the CAGFD shapes below easiest to remember.
Major 6 chords
Major sixth chords (6) can be used in place of major chords or major 7 chords. I think they sound airy and less tense than major 7 chords.
They are formed by essentially taking a dominant 7 chord and lowering the ♭7 a half-step to a 6.
Notice that the major 6 chord shapes are the same as the m7 chord shapes (with different roots).
Also note that there is no practical D shape for major 6 chords. (This is related to the fact that the D7 shape is rootless).
Minor 6 chords
Minor sixth chords (m6) can be used in place of minor chords or minor 7 chords. They are sometimes described as sounding dark and mysterious.
They are formed by essentially taking a minor 7 chord and lowering the ♭7 a half-step to a 6.
Notice that the minor 6 shapes are the same as m7♭5 and dominant 9 shapes (with different roots).
Dominant 9 chords
Dominant ninth chords (9) can be used in place of dominant 7 chords. They still have the tense dominant sound that wants to resolve, but compared to a dominant 7 chord I think they sound brighter and happier. Imagine the sound of a flashback dissolve in a clichéd TV show.
Because proper ninth chords have more than 4 notes, on ukulele some chord tones must be left out. In this case, the shapes used here are all rootless. They are formed by taking a dominant 7 chord and raising the root a whole step to a 2 (aka 9).
Note that there is no practical D shape for dominant 9 chords. (This is related to the fact that the D7 shape is rootless).
Also note that these rootless ninth chord shapes are the same as m6 and m7♭5 shapes (with a different root).
You could use this same approach for any chord type, really. These are just the ones I find most useful at the moment.
I usually practice these chord shapes in two ways:
To practice a variety of chord types: I focus on a single shape (like C) and play all the chord types in that shape (C, CMaj7, C7, C6, …) paying careful attention to the chord intervals and how they change to make different types. I use this diagram as a reference: CAGFD by shape.
To practice alternate chord voicings: I focus on a single chord (like Em or C7) and play it all over the fretboard in every shape, paying attention to where the shapes are in relation to each other. I use this diagram as a reference: CAGFD by type.
I hope some of this is useful. Enjoy!