Chords and Scales
The major scale as a chain of fifths
The major scale is usually written down as a series of major and minor seconds, but this disguises an important feature, namely that it can also be arranged as a series of perfect fifths.
The C major scale below is arranged starting on F (its subdominant) and ascends in perfect fifths up to B (its leading note). There is no other interval by which you can cycle through the entire major scale like this other than the perfect fourth (which is the inversion of a perfect fifth). You would need a mixture of major and minor intervals in order to cycle through the major scale using thirds, sixths, seconds or sevenths.
The chain of fifths is broken once you have used all the notes of the major scale: if you continued ascending in perfect fifths after the final B in the example above you would arrive on F#, which is not a note from the C major scale. To continue ascending by fifths within the scale of C major you would need to use a dimininished fifth to arrive on F natural.
This cycle of fifths, broken by the diminished fifth between the leading note and the subdominant is crucial to the way the tonal system works. Given the importance of notes related by fifth, it is interesting to note that the first interval in the harmonic series (after the first octave) is a fifth.
From the blue triangle below, you can follow links to information on how the cycle of fifths is also one of the most important relationships between triads in tonal music. The cycle also helps to understand how tonal music moves from one key to another, as discussed in keys and modulation.
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© Copyright Thomas Pankhurst