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Tetrachords divide all the musical tones into groups. These groups can then be used to construct scales.

Tetrachord means a perfect fourth. The last note of a major tetrachord is a perfect fourth above the first note. Coincidently, tetrachords consist of four notes. The half-step formula for a major tetrachord is: root, 2 half-steps, 2 half-steps, 1 half-step. Let's construct a tetrachord starting from the C note.

Tetrachord half-step formula: 2 - 2 - 1

To construct a C tetrachord start from the C note and count up two half-steps. Two half-steps above C is D. Count two half-steps above D to get an E. One half-step above E is F. So a tetrachord starting from C is: C, D, E, F. See the diagram below.

C Major Tetrachord Construction

C tetrachord construction

For another example construct a tetrachord starting from an A note. Two half-steps above A is B. Two half-steps above B is C#. One half-step above C# is D. So a tetrachord starting from an A note is: A, B, C#, D. See the diagram below.

A Major Tetrachord Construction

A tetrachord construction

The importance of tetrachords becomes clear in the lessons covering major scales and the circle of fifths. Practice constructing tetrachords for the remaining notes. Here are a few guidelines to remember when creating tetrachords:

  • Notes are always in alphabetical order
  • Some notes may need to be sharpened or flattened
  • There is only one of each note (F# - G, not Gb - G)
  • Don't mix sharps and flats
  • The half-step formula is: 2-2-1

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