Piano Clues

A tetrachord is a combination of four specific tones. “Tetra” means four and “chord” in this case just means: “a collection of tones”.

It’s not a chord in the sense that you use it to harmonize a melody. Blame the old Greeks for the terminology.

The interval formula for a tetrachord is: W W H

This means the first three tones are each a whole-step apart (W), but the distance to the last tone is only a half-step (H).

(Remember that a half-step is simply two notes next to each other, while a whole-step skips a key.)

Why would you want to know about a tetrachord? Well, you don’t really… but it’s fun anyway.

Here’s a trick: By stacking two tetrachords on top of each other, you create a major scale.

So if we begin at C and build a tetrachord, the tones are: C D E F

Then we skip a whole-step and build a second tetrachord starting on G: G A B C

Verify it for yourself: G to A is a whole-step, A to B is the second whole-step, and B to C is the final half-step.

That means a tetrachord is exactly half of a major scale. Which half? It doesn’t matter!

Here’s the fun part: if we build another tetrachord on top of this we get: D E F# G

Did you realize that we have just created the major scale of G?

If we build another tetrachord on top, we get the D major scale:

And so on… You can go clockwise around the Circle of Fifths this way until you get back to where you started.

This entry was posted on Sunday, January 6th, 2008 at 4:02 pm and is filed under Scales. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.