Tetrachord

A tetrachord is a four-note segment of a scale whose outer notes are a perfect fourth apart. The name comes from the Greek tetra, four, and chordē, string. Ancient Greek theorists described their scales in tetrachords, four notes spanning a fourth, and classified them by where the two inner notes fell.

The major scale as two tetrachords

The major scale splits neatly into two identical tetrachords, each with the step pattern whole, whole, half, joined in the middle by a whole step:

• Lower tetrachord: C D E F (W–W–H)
• The joining step: F to G (W)
• Upper tetrachord: G A B C (W–W–H)

▶Listen0:07

That gives you a quick way to build and check any major scale: two W–W–H groups, a whole step apart. In D, for example: D E F♯ G, then A B C♯ D.

Tetrachords and the circle of fifths

The upper tetrachord of one major scale is the lower tetrachord of the key a fifth higher. G A B C ends C major and begins G major; G major then needs a new upper tetrachord, D E F♯ G, which in turn begins D major. Each step adds one sharp, exactly as the circle of fifths does. Going the other way, the lower tetrachord of C major, C D E F, is the upper tetrachord of F major, which then needs a B♭ in its new lower half.

▶C major: G A B C on top0:07▶G major: G A B C below0:06

Minor scales and other shapes

Other scales combine other tetrachord shapes. The natural minor scale joins W–H–W (A B C D) to H–W–W (E F G A). The harmonic minor scale keeps the same lower tetrachord but has an upper one of half step, augmented second, half step (E F G♯ A), which gives it its distinctive sound. Modes can be described the same way: Dorian is two W–H–W tetrachords, D E F G and A B C D.

Why it helps

Thinking in tetrachords cuts a seven-note scale into two four-note chunks that are easy to remember and that fit naturally under four fingers. One way beginners play their first major scales is to split them between the hands: the left hand takes the lower tetrachord, the right hand the upper one.