Form a chord on the top four strings like so:

7th fret/D string
6th fret/G string
5th fret/B string
4th fret/ E string

(suggested fingering low to high is: 4,3,2,1)

Played in conjunction with an open A string the chord you are fretting is Amaj7. This chord is very sweet sounding and is popular in jazz, soul and r&b music.

Now pluck the four fretted strings again and quickly pluck an F#/Gb note (second fret on the low "E" string) using the thumb and index finger of your right hand.

Notice how even though the top four notes are exactly the same the chord has now taken on a completely different flavour, going from light and breezy to dark and bluesy. That's because you are now playing an F#min9 chord.

This is a perfect example of a "two-faced" chord or, in other words a chord whose complete sonic character is altered when played over different root notes.

Here's another:

7th fret/A string
8th fret/D string
7th fret/G string
8th fret/B string

(suggested fingering here low to high is: 1,3,2,4)

These four notes played over an open low E string form an Emi7b5 chord. Minor 7b5 chords are often used as a substitute II chord in a II, V, I sequence.

Now by altering our fingering and adding a C at the 8th fret on the low E string, we form a rich and (dare I say?) Kenny Burrell-esque voicing of the C9 chord.

(suggested fingering is: 2,1,3,1,4)

One final variation on this theme:

Transport the four fretted notes to this position on the top four strings:

2nd fret/D string
3rd fret/G string
3rd fret/B string
3rd fret/E string

(suggested fingering is: 1,4,4,4)

Notice how, when this shape is played against a low open E, it still sounds like an Emi7b5 (although the sound is a little different due to the thickness of the strings!) but by adding a G at the third fret on the low E string:

(suggested fingering is: 2,X,1,4,4,4)

We are rewarded with a dark and sexy voicing of Gm6.

This lesson is not meant to be an end in itself but, rather, I hope to inspire you to experiment (using the different techniques we've discussed) to find hidden sounds in other chords you thought you knew. Try putting different bass notes under other examples in your chord vocabulary. Some, maybe even most, combinations will be unpleasant but occasionally you'll hit on a sound that really knocks you out. When you do, try to work out the correct name for the chord and commit it to memory. This really is a great way to expand your knowledge of chords and arpeggios and you'll find that shapes learned this way seem to stick in the mind better than something you just picked up out of a book.