Inversion

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When the bass is not the same as the root, the chord is inverted.

The number of inversions that a chord can have is one fewer than the number of constituent notes. Triads, for example, (having three constituent notes) can have three positions, two of which are inversions:

• Root position

The root note is in the bass, and above that are the third and the fifth. A triad built on the first scale degree, for example, is marked 'I'

• First inversion

The third is in the bass, and above it are the fifth and the root. This creates an interval of a sixth and a third above the bass note, and so is marked in figured Roman notation as '6/3'. This is commonly abbreviated to 'I6' (or 'Ib') since the sixth is the characteristic interval of the inversion, and so always implies '6/3'.

• Second inversion

The fifth is in the bass, and above it are the root and the third. This creates an interval of a sixth and a fourth above the bass note, and so is marked as 'I6/4' or 'Ic'. Second inversion is the most unstable chord position.