The capo

Clamp a capo at the 2nd fret, play a G shape, and the guitar sounds an A chord.

A movable nut

A capo is a clamp with a padded bar that presses all six strings down at one fret. The word is short for the Italian capotasto, which originally meant the nut of a string instrument. That is exactly what a capo does: it makes a new nut further up the neck. With the capo at the 2nd fret, every open string sounds two semitones higher, and every chord shape you play above it moves up by the same amount. You keep the fingerings you already know and get a new key.

Shape name and sounding name

With a capo there are two names for every chord. The shape is what your fingers make, counted from the capo as if it were the nut. The sounding chord is what the audience hears. To find it, move the shape name up one semitone for each fret. The 12 semitones in order are C, C♯, D, D♯, E, F, F♯, G, G♯, A, A♯, B. A G shape at capo 2 goes G, G♯, A, so it sounds as A. A C shape at capo 3 goes C, C♯, D, D♯ and sounds as D♯, usually called E♭. Songbooks write this as "Capo 2" at the top and print the shapes, so you can read the chart without doing the sum.

Why players use one

The main reason is the voice. If G, C and D put a song too low for the singer, a capo at the 2nd or 3rd fret lifts the whole song into a comfortable range while the guitarist keeps the easy open shapes. The second reason is sound: open strings ring longer and brighter than fretted ones, and a capo keeps that ringing quality in keys like E♭ or B♭ that would otherwise need barre chords. A third reason is texture. When two guitars play together, one can play open shapes and the other the same chords with a capo further up, so the chords sound in two different positions at once.

A capo changes only the open strings. A note fretted above the capo is the same note it was before; the 7th fret of the low E string is still B. That is why a capo is quicker than retuning. Put it on right after tuning, close behind the fret, straight across, and then check the tuning again, because a capo pressing unevenly can pull strings slightly sharp.

Try it

The chord player has no capo, so it plays the sounding chords. Press Play to hear A, D, A, E: this is exactly what G, C, G, D shapes sound like with a capo at the 2nd fret. Compare it with the G, C, G, D player in the last unit.