Every chord has a mirror twin. Reflect its notes around the axis that sits between the root and its fifth and a MAJOR chord flips into a MINOR one — the same harmonic ‘weight’ seen upside-down. Jacob Collier made it famous, but it’s just symmetry: the tonic-dominant axis is a line, and reflection is a mirror. Slide to reflect the chord and watch major become minor.
Negative harmony reflects pitches about the AXIS midway between the tonic and its perfect fifth — here at 3.5 semitones (between the minor and major third). The reflection map is p → 2·axis − p (mod 12). Apply it to the C major triad {0, 4, 7} and you get {7, 3, 0} — whose interval structure {0, 3, 7} is a MINOR triad: major and minor are mirror images across the tonic-dominant axis, and the whole functional weight of a progression can be reflected to its ‘negative’. A fail-loud self-check throws unless the major triad reflects to a minor-triad interval structure. ◆ real music theory, node-verified.
The Levy/Collier tonic-axis reflection (the exact p→2·axis−p map turning major↔minor); which axis you choose is a convention and ‘same weight’ is an interpretive claim — the major-reflects-to-minor symmetry is exact.