# Tetrachords

# Tetrachords

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**

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**

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