Last time I made a lesson on how to use a guitar capo, I left out an important bit of information: how to transpose chords properly so that you remain in the same key as the rest of the band.
Today that's what we're talking about.
The rule of thumb that I get into in the video is basically this:
If you move the capo UP X number of frets, you need to transpose your guitar chords DOWN by the same number of semitones.
Each fret is a semitone, right? So in order to maintain the balance, if you go up with the capo, you need to go down with the letter names of your open chords.
This might be a bit confusing, but keep in mind you're not actually changing keys. The only sense in which you're changing keys is in that you're changing to the open chord shapes of a particular key. The whole idea is to remain in the same key right?
Let's do an example.
Say the song is in the key of F, but you don't want to deal with those pesky bar chords.
Thankfully, you have a capo that you can use to transpose the chords with, and you have a clever idea to use the chords from the key of D, transposed up!
To figure this out, you need to find a location on the fretboard where an open D major chord shape becomes an F.
If open position gives you a D, then if you placed the capo on the first fret, it would turn that D into a D#, right? Everything moves up by one semitone. That gets us closer, but we need two more frets to get to F (the distance from E to F is a natural semitone - if that doesn't make sense please watch this).
Therefore, if you capo at the third fret, you can play an open D major chord shape and it will give you an F major chord.
This means that anytime the song has an F chord written, you need to play a D chord instead (with that capo on the 3rd fret, of course.)
In like manner, every other chord in the key needs to be transposed in the same way, so let's do that too. Here are the six main chords in F major:
F Gm Am Bb C Dm
To transpose the chords correctly, you need to move each chord by the same distance that you've moved the F, which is three semitones (three frets). This becomes:
D Em F#m G A Bm
How To Simplify Transposing Chords With A Capo
The musical number system - sometimes called the Nashville number system - makes this process much easier.
The six chords I mentioned can be assigned numbers (Roman numerals), according to their position in the scale.
In any major key, the I, IV and V chords are major, and the ii, iii, and vi chords are minor. We use lower case numerals to show minor, and upper case for major.
So, we could write the key of F like this:
Now each of those chords has a number, and we can do the same thing for every key. Once we've done that, we could literally write a song using just numbers, and then instantly transpose it into any key using this system. Here's the same chart with D major added: