Talking about major and minor keys, as we did last week, inevitably brings up a question: “How do you mark minor keys’ key signatures? All we covered in the key signature lesson was major keys.”

The answer: To find out any minor key’s key signature, you have to know which major key it’s related to.

Mapping Out the Keys’ Family Tree

For every major key signature, there is a minor key which uses the exact same signature, because it uses just about the same scale (set of 8 notes). The only real difference is that the minor key scale begins and ends on a different note. When we talk about these minor keys in comparison with their similar major keys, we use the term “relative minor.”

(I’m not exactly sure why the people who created modern Western music notation chose to note minor key signatures this way, but it probably saved time and brain space. Instead of having to make 12 major key signatures, then make 12 more key signatures for minor keys, they used each key signature twice, because each major key already had a minor key that was very similar to it.)

To find any major key’s relative minor, simply go down three half-steps from the major key’s beginning note (the note it’s named after). For instance, say we’re trying to find the relative minor of C major, below:

Begin on C (the note circled in red on this graphic)…

…and go down in pitch (to the left on this graphic) 3 half-steps. In this case, you’ve landed on A. This tells you that A minor is the relative minor of C major.

What Has This Got to Do with Key Signatures? A Lot, Actually

So, for instance, when you see the key signature for G major (at left), for instance, the ensuing music might not actually be in G major–it might be in the relative minor key instead. (What is the relative minor of G major? Remember, count three half-steps down from the original key (G major), and you’ll find the beginning note (or keynote) of the relative minor.) Answer: Below G is F-sharp, then F, and finally E…and E minor is the relative minor of G major. E minor is thus given the key signature of one sharp.

One Important Caveat: That Pesky “Sharped Seventh Note” Again

Remember last week when I discussed that minor key scales are created by taking the major key scale, flatting the third and sixth note, then sharping the seventh–except that the “sharped seventh” is really in the same place as it is on the major key scale? Well, that comes into play here.

When you play the relative minor key, it’ll be the exact same scale as the major key it’s related to, except that the seventh note will be sharped. That change is not reflected in the key signature at all–it’s just something you have to remember. Take the key of A minor, for instance; it’s related to C major, which has no sharps and no flats. But when you play something in A minor, the seventh note is a G-sharp, because that’s just how minor key scales are constructed.

The Complete Key Signature Family Tree: The Circle of Fifths

To remember and reference all these various major-relative minor matchups, music theorists have come up with a cool little graphic called the Circle of Fifths, seen below (this was retrieved from line6.com):

Names of major keys appear on the outer “ring” of this graphic, while their relative minor keys appear synced up with them on the inner “ring.” This really helps as a memory tool!

Next Week: A Look at REAL Sheet Music

Now that we know a good bit about the way music is notated, let’s see how to apply that knowledge to real sheet music. That challenge appears next Saturday!