What is a tetrachord, and how many tetrachords are in a major scale?.... :think:

A tetrachord is the first four notes in a scale. There are two tetrachords in a scale.

Example:

The first tetrachord of the C scale would be

C-D-E-F

The second

G-A-B-C

The second tetrachord is always the first tetrachord of the scale of the fifth scale degree. I.e. The second tetrachord of C is the first tetrachord of G.