Keys can be seen as families of notes and chords (
visualize it here). Because of the tuning and design of the guitar, some keys are easier to get around than others. Capos come in very handy because they can make it seem, to your fingers and brain, that you've changed from an unfriendly key to a friendly one ... without actually changing key. The chart and lesson below will show you how. The chart can also be used to 'transpose' a tune to a new key, if for example, you learn a tune in one key, then meet a singer who prefers to sing it in a different key.
The blue row at the top shows the 12 major keys of music; the blue column to the left shows the 7 notes of the major scale and the chords that comprise the key. The Roman numerals indicate the flavors of the chords built on each scale degree. Upper case means 'major'; lower case means 'minor' ... apart from the vii chord, which is diminished. Each grey column is a key.
Looking at the key of C (4th grey column from the left), you can see that its scale is (you have to read from top to bottom) C - D - E - F - G - A - B and the seven related chords are C - Dm - Em - F - G - Am - Bdim. All keys work the same way.
How to use the chart
Find out first what key the original tune is in. As an example, let's say it's F#, an awful key for guitar, as it throws up so many barre chords.
Look to the left of the difficult key until you find the key you want to play in, let's say C. Looking to the right won't work, because the new key HAS to be lower in pitch than the original, since the capo will be clamped higher up the fretboard. Then
Count the number of columns it is from the original and
put your capo on that fret. So, in this example, C is 6 columns away from F#, put your capo on the 6th fret and play as if in C.
Keep referring back to the original key to see which chords are in the tune, and move along the row until you get to the C column. You'll then see which chord is required. Retain the original quality of the chord, so if it was major, make it major; if it was minor7th, keep it as minor7th. (The Roman numeral chord flavors are not necessarily the ones required as deviations from the key are often used by the composer of the piece of music.)
Transposing eventually becomes second nature, as you will begin to see tunes as a series of roman numeral chords. What's more, you'll be able to hear them as roman numerals. The most important thing to remember is that there are only 7 chord letters and they are in alphabetical order: A B C D E F G. Think of them in a repeating circle so that A follows G.
Notice how the key of C is made up of all the natural notes - no sharps or flats.
If you are playing with another guitarist, it's often a good idea for one of you to play with a capo on, as if in another key. For example, one of you in C -- the other with a capo on the 5th fret playing as if in G. The effect is a more interesting interplay of notes and a janglier sound, as each player is playing the same chords in different positions, giving the overall sound a much wider range.
Here's an example of a chord progression that has been transposed
This progression is similar to the old blues tune "Nobody loves you when you're down and out". I used it because it's probably vaguely familiar to most of us. I've written it out in the key of F# to begin with, an unfriendly guitar key, and as you can see, it's not a pretty sight. It's a daunting task to follow them all, and all are barre chords.
The way around this less-than-friendly progression is to turn it into a guitar key. Let's pick C. Referring to the chart, the C column is 6 away from the F# column. So, we put our capo on the 6th fret and play as if in C. We've retained each chord's rank in the key (Roman numeral/row) and its original flavor (as in major - minor -7th), and we get:
Much easier to get the fingers around, as all except the F are open chords. We could also have put the capo on the 4th fret and played as if in D, or the second fret and played as if in E.
Transposing ...
If you simply wanted to transpose the tune to C, actually change keys from F# to C, then don't use the capo ... just play it in C.
You can also transpose using a capo but you can only go up in pitch. For example, you've learned a tune in C and you now want to play it in Eb ... Eb is an awful guitar key, so
look to the right of the key you're in (C) and count the number of columns to Eb ... 3. Clamp the capo on the 3rd fret and you can now play all the same chord shapes from C, but play the tune in Eb.
