If you're starting out your journey as a singer/songwriter and you play guitar you'll more than likely find yourself using a capo to learn the songs you want to learn. If you're not starting out as a guitar player, you'll probably want to know how a capo works anyway as it makes all the difference in the world when you're play with someone who does use a capo.
A capo exists to make it easier for you to change the key of your song. Last time we talked about the six chords in every key. A capo let's you change the key without changing the chords you're playing, or alternatively it can change the chords you're playing without changing the key. Let me explain.
Basically you would use a capo for these two reasons:
1. To change the key of the song to a more comfortable key, for example for your vocalist.
2. To change the chords you're playing to more comfortable and playable chords while keeping the same key.
By putting a capo on a fret, it's as if all of those strings are already automatically being pressed. Looking at how a guitar is played, usually a guitar player presses down on the fret board with their left hand to make a chord. What this pressing really does is shorten the length of the string vibrating from the full length of the string to a new shortened length. This length is exactly from the bridge of the guitar to where the fingers are pressing. Each fret on the guitar represents what's called a half-step, like each key on the keyboard. So if I strum all of the open strings on a guitar in regular standard tuning, those open strings happen to make an Em11 chord (E A D G B E). If I put a capo on the first fret, it moves all of those notes up a half-step and makes an Fm11 chord (F Bb Eb Ab C F).
If you're trying to learn a new song, and that song is in the key of G# but you don't want to have to think about chords in the key of G#, you can just put a capo on the first fret and think of those chords as being in the key of G. G is a much easier key on the guitar. Or you can put the capo on the 4th fret and think about those chords being in the key of E. In general for every fret up the guitar that you put this capo, you can think of the chord shapes moving down one half step while the key stays the same.
Chords like G, C, D, Em are so popular for a reason. They're easier to play on guitar than chords like F or B. You can use a capo to change the chords demanded by your song to other chords that are easier to play.
If you're learning a song and the melody feels uncomfortable to sing, you can keep the chord shapes the same and change the key by using a capo. Keep in mind that a capo is usually thought of as raising the key (typically this is not helpful for making something easier to sing), but capos can work to lower the key too:
All you need to do to lower the key is to go up higher with the capo and then sing down an octave from there. Makes sense? So if I'm singing in the key of E with no capo and I want to sing in the key of C using the same chord shapes, I can move the capo to the 8th fret and still play as if I'm in E but it's now going to sound like C thus making it easier to sing.
If you're playing guitar, the easiest way to play with someone is to get a capo and match them. If you don't have one or don't want to do it, the easiest way is to look where their capo is and do a quick mental calculation of what key you need to play. So if I was playing with someone and they're playing G C and D chords but they're on a 5th fret capo, then I know I need to subtract five half-steps from the chords they're playing to find the 'real' chords. The real chords are sometimes called the 'concert' chords and just refer to the actual pitches sounding form those chords, not the chord shapes that the capo user is using.
Let's take each of those chords down 5 half steps: G down 5 half steps is D, C down 5 half steps is G, and D down 5 half steps is A. That means they're playing in the key of D and I can play D all day long while they're playing in G and everything's good!
Hopefully this helps make capos make sense. We always use them, but hopefully this makes you understand them and makes it make sense. If you have a question, feel free to drop us a line at firstname.lastname@example.org. We'd be happy to answer it or make a new post like this one!