Inversion

What it means

“Inversion” is a collective term for three different procedures that carry the same name in music theory. They have in common that something existing appears in a changed arrangement, but each concerns something different: a chord, an interval, or a melody. The entries Chord inversion and Interval inversion treat the first two in detail.

Musical use

With chord inversion, not the root but a different chord tone lies in the bass. The chord stays the same and keeps its name; only which note lies at the bottom changes. From the triad in root position arise in this way the six-three chord and the six-four chord, from the seventh chord the six-five chord, the third-fourth chord, and the second chord.

With interval inversion, the lower note of an interval is placed an octave higher. In the process the interval changes its designation: the numbers of both together add up to nine, major becomes minor, augmented becomes diminished, perfect stays perfect.

With melodic inversion, a sequence of notes is mirrored: every step upward becomes an equally large step downward. This transformation belongs to the procedures of counterpoint and of motivic work. In the fugue, the subject can appear in inversion; the counter-fugue makes this the principle of the answer, the mirror fugue mirrors the whole texture. Together with the retrograde, inversion yields the retrograde inversion.

Which meaning is intended results from the context: is the discussion about a chord, a dyad, or a line?

The third meaning concerns melodic inversion, in which all the intervals of a line run in the opposite direction: what rises falls, what falls rises. It is used in the fugue, in the canon, and in twelve-tone technique, and serves there as a means of processing that creates kinship and contrast at once.

Performance practice

When reading theoretical texts, first clarify which of the three meanings is intended. Practise chords in all inversions and listen to how their weight changes. And look, in contrapuntal music, for inverted entries of the theme; they are often harder to hear than to see.