I recently read an interesting article about how many guitarists are comfortable in certain keys (typically C, G, D, A and E). However, when we move to another key (F or Db), we are not so sure of our chord choices.
Of course we could crank out a nice little chart to remind ourselves of the common chords for a given key…
However this article proposed a different solution. It’s called the “circle of fourths and fifths“.
The concept this diagram attempts to communicate is the relation of the tones to one another in a given key. Fig 1 shows the relation of one key to another. If we move clockwise around the circle, we move a fifth for each movement. G is a fifth from C and D is a fifth from G, etc.
If we move counterclockwise, we move a perfect fourth. So F is a fourth from C and Bb is a fourth from F and so on.
Great! So how can we use this information? In most songs, the I-VI-V chords are the primary chords used. For example, the song “Mighty To Save” by Hillsong. The entire song is I, VI, V, and VIm chords. If you look at Fig. 2, you can see that the I chord or root is at the top, the IV is to the left of the root and the V is to the right. Inside the circle is the related minor chords to the root.
So, if we are in the key of C, the V chord is to the right of C (a perfect fifth from C) and the IV chord is to the left of C (a perfect fourth). And the VIm (Am) is inside the circle below the C. If we want to change to the key of F, we can move the F to 12 o’clock and we can see that now Bb is our IV chord, C if our V chord and Dm is our VIm chord. By spinning the circle of fourths and fifths to show the desired key at 12-o’clock position will show you the related chords for any key.
You can read more about the Circle of Fifths at wikipedia.