Identifying the Key of a Piece of Music

The concepts in this blog post refer to Lessons 15 and 23 of the “Easy Music Theory with Gary Ewer” Course.
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If you’re looking at a piece of music that has no sharps and no flats, how do you know if it’s in C major, A minor, or perhaps some mode?

Let’s deal with the question of mode first. We know that a scale that starts and ends on D, but uses the key signature of C major, gives us the dorian mode. From E to E is phrygian, F to F is lydian, G to G is mixolydian, A to A is aeolian, and B to B is locrian. (These are all transposable to different key signatures, of course). For a piece of music to be in any of those modes, you’ll see the letter name of the mode playing a significant role, perhaps as the starting note, and most certainly the end note.

It’s more likely that the key will be either major or minor. So in the example of an excerpt of music that uses no sharps or flats, follow these steps to identify the key:

  1. Consider first the possibility of A minor. In order for the music to be in A minor, there needs to be a leading tone (G#) present. If you don’t see it, A minor is very unlikely.
  2. Confirm by looking for G-naturals. If you see G-naturals instead of G#s in the music, you are confirming that A minor is not possible.
  3. Look for a final note of C, especially approached by B below or D above.

There can sometimes be complications with this method, especially if the music includes sharps and flats that are operating as so-called “non-chord-tones.” But this 3-step method can at least get you close.

Written by Gary Ewer


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