Anatomy Room
Contrapunctus a 3

／Contrapunctus inversus a 3

Inverted mirror fugue with 1 theme, 3 voices, 4/4 beat, 71 bars each

Fuga a 2 Clav.／Alio modo Fuga a 2 Clav. on the nineteenth of the art of
fugue are the pieces arranged from this piece for two keyboards, adding
one free voice.

Mirror fugue is a piece that makes it possible for the whole piece to be
inverted. The image and the mirrored image are printed side by side on both
sides in the first edition of the art of fugue.

As we already saw in Cp.12, one voice was reflected another like soprano→
bass, alto→tenor, tenor→alto and bass→soprano, however, the mirrored
image in this piece goes like soprano→bass, alto→soprano and bass→alto.
So precisely speaking, this piece can be said that each voice is invertible by
double counterpoint at eighth degree, rather than saying the inverted form
of the whole piece. (see experiment 1)

This piece is the mirror fugue, and, on the other hand, it is the inverted
fugue. The response takes the inverted form of the theme as well as Cp.5 
and so forth, and the theme of the mirrored image that the whole piece is
inverted is equal to the response of the image.



The inverted common theme is varied and embellished by the theme of the
image. Now you can see the original form of the theme in blue in the upper
column (an image) in the music above. The following explains only the image.

The motive at the tail of the theme is often used as sequence. As for the
sequence from bar 14, the motive is passed to bass and goes on and on.



The sequence by the same motive can be found from bar 23, 41 and 51
followed by the thematic exposition, characteristically repeating in both the
basic form and the inverted in turn.

Now you can find the theme partially in soprano between bar 27 and bar 28,
making stretto with the theme in bass from bar 28.



The sequence from bar 51 varies its figure a bit and the motive in blue in
the music is relayed to bass at bar 58. Already mentioned in Cp.7, sequence
is closely related in its context from time to time, and here it also makes a
flow toward the cadenza at bar 59.



Such structure as seemingly binding free voices contributes to the organic
connection among each voice and also to the oneness for the whole piece.

Anatomy Room