A mandolin is tuned like a fiddle. Low note to high, the strings are G, D, A, E.
The a guitar is tuned E, A, D, G, B. The bottom four strings -- high to low now -- are G, D, A, E.
With apologies to James Watson and Frances Crick, the similarity has not escaped our notice.
A mandolin is a guitar, upside down. (So, therefore, is a fiddle.) Actually it's a bass upside down, since a bass is the bottom four strings of a guitar.
This can be a huge help if you're a guitar or bass player trying to read mandolin chords, and a great memory aid if you're a guitar-player migrating to mando.
For example?
Okay, that full, ringing G chord: A middle finger g, third-fret the E string, an index-finger b on the second fret of the A string, an open d and an open g. Play it on the mando, then hold up your instrument, flip it over from top to bottom and it looks exactly like the bottom of your guitar-player's G chord.
Move those two fingers to the same spot on the middle two strings and you have a C chord. Flip it upside down and you'll see the bottom of a guitar's C chord, though with different fingers.
D's a little harder to see, because not all guitar players wrap their thumbs around the neck to fret that low f#. If you do, though, you'll suddenly see that your two-finger a/d/a/f# on mando is just like the f#/a/d/a on guitar.
Closed-form chords are harder to decipher like this because the fret-spacing lets a mandolin player get his fingers to frets that a guitar player could never reach, but there's usually at least a piece of the chord shape that's recognizable, if you stand on your head.
I encourage you to work through the rest of the chords yourself. It's fun.
