This is the major scale of C: C D E F G A B C
This is the natural minor scale of A: A B C D E F G A
Notice anything? That’s right, they both use the same tones!
When the tones in a piece come primarily from the C major scale, we say that the piece is “in the key of C major” or just “in the key of C”.
When the tones in a piece come form the A natural minor scale, we say that the piece is “in the key of A minor”.
Since both of these scales contain the same tones, the key signature of both the C major key and the A minor key are identical: white keys only, no sharps or flats.
Because of this, the key of A minor is called the relative minor of C major.
Conversely, C major is called the relative major of A minor.
Finding the relative key
Here are the rules:
- The 6th tone from a major scale names its relative minor.
- The 3rd tone from a minor scale names its relative major.
The 6th tone from the C major scale is A, so A minor is the relative minor of C. The 3rd tone from the A natural minor scale is C, so C major is the relative major of A minor.
If you’ve read the article on inverting intervals, this should make sense to you because: 9 – 6 = 3 and 9 – 3 = 6.
You can also count it out in half-steps:
- To go from major to relative minor, go three half-steps down.
- To go from minor to relative major, go three half-steps up.
What is the right name?
From the key signature alone it is impossible to find out which key — major or minor — you’re really in. You’ll also have to look at the melody tones and at the chords.
Pay attention to the following:
- The name of the piece. If it’s called “Sonatina in C major”, it’s probably in C major.
- If the piece begins or ends with a major chord, it is most likely in a major key.
- If the piece begins or ends with a minor chord, it is most likely in a minor key.
- Most of the time, the melody tone the piece ends on names the key. So if the choice is between the keys of C major and A minor and the piece ends on a C tone, then the answer is C major.
- If the melody contains accidentals (sharps and flats that are not in the key signature) then you could be in a minor key. The harmonic and melodic minor scales may be used for the melody and chords, and they contain sharpened tones.
Note: often a piece begins in minor but ends in major. Somewhere along the way it “modulates” from the minor key to the relative major key. It starts out sad but ends happy.
Songs that begin in major will often switch to a minor key on the bridge (this may be the relative minor, but it could also be another minor key) and then modulate back to major for a new verse or the chorus.
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