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Music theory

Created: 2017-12-10 15:19:53 -0800 Modified: 2018-01-14 12:26:22 -0800

  1. Tonic
  2. Supertonic
  3. Mediant
  4. Subdominant
  5. Dominant
  6. Submediant
  7. Leading tone (leads back to tonic). This is always a diatonic half step below the tonic. In a minor key without a raised seventh (e.g. natural minor), the seventh scale degree is called the subtonic and is a diatonic whole step below the tonic.
  8. Tonic

The mediant is a modal degree; it determines whether a scale will be major or minor.

The mediant is halfway between the tonic and the dominant. The submediant is halfway between the subdominant and the tonic. For example, in the key of C, the subdominant is F, the submediant is A, the tonic is C, the mediant is E, and the dominant is G, so they form the set of thirds F-A-C-E-G.

  • Triads
    • Root is blank or 5 3
    • 1st is 6 or 6 3
    • 2nd is 6 4
  • Seventh chords
    • Root is 7
    • 1st is 6 5
    • 2nd is 4 3
    • 3rd is 2 or 4 2

The numbers come from which intervals appear above the bass, so there’s nothing to memorize. E.g. looking at C first inversion, we have E G C. E to G is a third, and E to C is a sixth, so it is 6 3.

For seventh chords, it’s a little more difficult because there are only two numbers but three intervals. It seems that we always out the interval to the tonic (if possible) and the leading tone (if possible).

CEGB: 7 (bass - B is a 7th)

EGBC: 6 5 (bass to C is a 6th, bass to B is a 5th)

GBCE: 4 3 (bass to C is a 4th, bass to B is a 3rd)

BCEG: 2 (bass to C is a 2nd)

The circle of fifths and the mnemonic “French Colonel Goes Down And Ends Battle” is enough to figure out how many (and which) sharps or flats are in any key.

For example, C has no accidentals. Going a perfect fifth up to G will add one sharp: F (as in “French” above). Another 5th up gives us D, which has two sharps: F and C.

For flats, we reverse FCGDAEB to get BEADGCF. Going a perfect fifth below C gives us F, which has one flat: B. Another 5th down will add E flat, another for A flat, etc.

When drawing a key signature, the order of sharps and flats follows the same mnemonics above.

A quick trick to identifying major key signatures:

  • For a signature with sharps, the key is a diatonic half step above the last sharp in the key signatures. For example B major has 5 sharps, the last being A#. A diatonic half step above A# is B.
  • For a signature with flats, the key is the second to last flat. For example, Db major has 5 flats, the last being G flat. The second to last is Db, and that itself is the key.