The circle of 5ths is an iconic piece of music theory that pops up from time to time. It has a couple of practical purposes like figuring out what key a piece of music is in, and navigating a particular chord progression commonly called 'going around the horn.'
Here it is:
General DiscussionReading the chart clockwise, you progress from one chord to the chord that would be the V to its I. In other words, G is the five chord for C, D is the five chord for G. etc. Starting at C, you can also see that the key signature keeps adding a sharp at every step. As we noted in the post about scales, the sharp that gets added corresponds to the 7th note in the scale for that key. If you start at the top and go counterclockwise, you are going to the IV chord and the flat you are adding is, coincidentally, the fourth note of the new scale. So we go from C to F, and the flat is Bb.
I don't show the minor keys, but remember from a previous blog that a major key's relative minor has the same key signature. And the relative minor is the note that corresponds to the 6th note of that scale. So the relative minor of C is Am, the relative minor of G is Em, etc.
Don't get too overwhelmed by all the keys and their signatures; as we talked about earlier, the main keys for bluegrass are C, G, D, and A. If you have a blues guitar player in a jam, you'll do some stuff in E. And I find it's good to know the scale of F major--cause every now and then someone wants to drag out some old folk song in D minor (F's relative minor).
Another use for the circle of 5ths, I discovered, is deciphering modes. In my next blog post, I will talk about modes, and having the circle of 5ths handy can let you figure out a modal pattern in any key very quickly.
Around the HornSometimes a song has a progression that sounds 'different' and if you ask about it, some veteran might say "Oh it just goes around the horn." A good example is "Salty Dog." The progression is:
G, E, A, D, G. (In Nashville notation that would be I, VI, II, V, I.)
It feels good because these are mainstays of a scale--for the most part. But it sounds 'different' because it uses two major chords where the natural chords would be minors. Specifically, I am referring to the E major instead of the E minor and the A major instead of the A minor.
Once you jump to the VI chord, the progression goes counterclockwise along the circle of 5ths until it gets back to the I chord. One way to think of it is to ask yourself "This chord I'm on is the five chord for who?" If that seems a little awkward, ask yourself "Who is the four chord of this chord?" (The circle of 5ths goes clockwise; when you go counterclockwise it is called the circle of 4ths--I'm not making this stuff up.) Personally, I like thinking in terms of "who is the four chord?" but I've had purists get mad at me for thinking that way.
So once you successfully make the jump to the VI chord, just take the circle of 5ths back to the root chord and you have gone "around the horn."
Example: Key of C going around the horn.
Start on C and jump to the VI--which would be A major (not hard to remember because Am is the relative minor and I think most of us know that.) OK, from A go to D (the four chord of A or the chord for which A is the five chord), then from D go to G (same reasoning) and from G go to C and you have gone around the horn.
And Now, Just for Fun (nothing useful, just mental chewing gum)Since there are only five black keys on a piano, you would think that the most sharps or flats a key could have would be five. But look at the bottom of the circle at F# and Gb. Each has six sharps and six flats respectively. What's with that?
Well, there is a simple rule for any scale: it has to use all the letters from A to G and can only use each letter once. So if you start your scale on F# what do you call the 7th note--the one that lands a half step below F#? You might be tempted to call it F or F natural, but you have already used the letter F in your scale (to name the 1st note F#). Well, that note might sound like F and if played on a piano might look like F, and if fretted on the 1st string of a Dobro would be on the third fret, but in the context of the scale of F# we call that note E#. And if you write music for a song in F#, every time you play that note, you write it as an E. The key signature tells the player to sharp the E and that means playing an F.
Now just for fun, who's the oddball in Gb?