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Even Numbers
| So far we have used only odd numbers to describe chords. | |
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| For over 500 years music theory has described harmony in terms of chords based on the interval of a third, 1 - 3 - 5 - 7 - etc. This is called tertian harmony. A theory that chords are built on fourths is called quartal harmony. These chords can be analyzed in tertian harmony but not with only odd numbers. |
Chords built on thirds:
Chords built on fourths: |
| For this and other reasons, even numbers are sometimes used. | |
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| C13: The 7th (Bb) makes the A a 13th. C6: In the 6th chord the seventh is absent. Notice that this chord is also Am7 in first inversion. C6add9: A "final" chord with the 6th instead of the 7th. Remember the overtone this note represents is between the 6th and 7th. D7sus4: The sus4 takes the place of the third. The sus stands for "suspension". |
Esus2: The number 2 may appear as sus when substituted for the third. Eadd2: The entire triad is present so the word "add" is used for the second. To use a "9" would imply the presence of the 7th (or 6th). E9maj7: Even though the third is missing, the presence of a 7th makes this a 9th. |
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