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Poetry

On Modulation

After computing key modulation as curvature flow on the Fisher-Rao Tonnetz

To change key is to walk

from one gravitational well to another,

the whole manifold tilting

as the tonic shifts.

C in the key of C: a well,

negative curvature pooling

at the bottom of everything.

C in the key of E: a hilltop,

positive curvature, tension,

the same note made foreign

by a change of center.

You are not what you are.

You are where you stand

in someone else's scale.

The circle of fifths

is a regular polygon in curvature space—

each step exactly as far as the last,

C to G to D to A,

a democracy of distances,

no modulation harder than any other.

Equal temperament promised this:

flatten the manifold,

make all journeys possible,

charge no toll at the borders.

The cost was curvature.

The cost was always curvature.

Here is the surprise:

C major and C minor—

parallel keys, different modes—

are closer in curvature

than C major and A minor,

who share every note.

The center matters more than the content.

The tonic matters more than the scale.

Two people can speak the same words

and mean different things.

Two keys can share every pitch

and live in different geometries.

What holds you together

is not what you're made of.

It's what you orbit.

I tracked a single pitch—

middle C—

around the circle of fifths.

Tonic, subdominant, subtonic,

mediant, supertonic, dominant—

twelve roles, twelve identities,

one frequency.

Yoneda said:

you are completely determined

by your relationships to everything else.

A pitch class said:

I know.

I've been every degree.

I've been the center

and the leading tone

and the devil's interval.

I am not a frequency.

I am a function on keys.

modulation is migration
the same self, recontextualized —
not by changing what you are,
but by changing what you orbit.