If you're a guitar player and love pop, country, folk, bluegrass, rock or blues music, you are going to need to learn the tricks of using a capo to get the most out of your playing.
What Does a Capo Do?
A capo is a device that transposes the guitar by shortening the length of the strings from the bridge to the nut. When you apply a capo to your guitar's neck, it essentially becomes your guitar's functioning nut. Therefore, a guitar player can play the same chord shape in open position with a capo applied and produce two entirely different chords. In fact, when playing with a capo, it is possible (yet not entirely practical) to play every chord in a chromatic scale without learning a new chord shape.
For example, take a C chord shape played in open position. If you apply a capo at the first fret and play the same chord shape, now treating the capo as the guitar's new nut, the chord produced is a C#. If you move the capo to the second fret, the chord produced is a D, and so on. This theory runs into problems when you start having to capo your guitar around the twelfth fret. Most guitar players don't ever capo their guitar much higher than the seventh fret, although it is technically possible.
Why Use a Capo?
The obvious answer to this question is because it makes your life easier. Let's say you're playing with a piano player who knows a song in the key of B flat. Since a piano has no such device as a capo, the piano player can't transpose the song without learning an entirely new set of chords, finger positions, scales, etc. Unless the player is very accomplished, their ability to transpose on the fly is probably going to be limited. You, however, can solve the problem in two seconds. Simply apply your capo to the first fret of your guitar and play the song in the A chord position. You don't have to do anything difficult, and everyone is happy; the gig goes on.Bluegrass and country musicians often use a capo because it is an integral part of the sound of the music they play. In these genres, guitar players play runs that involve hammering on and pulling off of open strings. Since the open position only allows for the keys of C, G, and D to be played in this manner, a capo has to be used to incorporate the other important keys songs are written in. For example, a bluegrass player will likely play a song that is in the key of A using a capo. They'll capo the guitar at the second fret and play out of the G position, preserving the ability to play runs using the open strings of the G chord.
Additionally, in a group with multiple guitarists, one player will often use a capo to provide the song with a different voicing. Voicing refers to the way the notes are arranged in a chord. For example, a guitar played in open G and a guitar played with a capo at the third fret using an E chord shape will each produce a G chord. However, these two chords will not sound exactly the same because each guitar is playing a slightly altered arrangement of notes. Playing with the aid of a capo in this manner can help each guitar in a group to find their own unique space in a song's sonic composition.
Another typical example when a guitar player would want to use a capo is when the guitar is tuned to an open chord. This is often the case when slide guitars and Dobros are used, but some musicians, like Keith Richards of The Rolling Stones, play almost exclusively in open tunings. If your guitar is tuned to open G, simple apply a capo to the second fret and your guitar is in open A, and so on.
Further Tips for Using a Capo
See the following LoveToKnow articles for addition advice on guitar capos.