Modal cadence formulas (clausula vera, Phrygian) and musica ficta

The standard 'clausula vera' (true cadence): one voice ascends by step to the modal final while another descends by step to the same final (or octave), expanding from a major 6th to an octave (or minor 3rd to unison). When the natural scale degree a step below the final is a WHOLE step rather than the half-step a leading-tone effect requires (true for Dorian, Mixolydian, Aeolian finals), musica ficta raises that note by a chromatic half-step. This is NOT needed in Phrygian mode: the note above the Phrygian final is already a natural half-step, so the descending voice's F→E (in E Phrygian) uses the mode's own natural half-step with no ficta, while the ASCENDING voice moves by a WHOLE step (D→E) — the distinctive Phrygian half-cadence, asymmetric unlike the ficta-raised Dorian/Mixolydian/Aeolian cadence where both approaches are half-steps. A second ficta rule ('una nota supra la, semper est canendum fa'): B is lowered to Bb whenever it would otherwise form or outline a tritone against F. Ficta must never alter the modal final itself, and a cross-relation (one voice's natural form against another's simultaneous/adjacent ficta form) must be avoided.

A Dorian cadence where the penultimate note approaches the final by a WHOLE step with no ficta raise — fails to produce the expected clausula-vera half-step pull. Separately, a Phrygian cadence incorrectly ficta-raised as if it needed the Dorian treatment — an over-application to the one mode it doesn't apply to.

Standard Renaissance modal-counterpoint pedagogy (as codified for teaching by Jeppesen's Counterpoint); outside Gould/Read/Ross/Stone's scope, flagged as such, directly relevant to Gradus's modes curriculum.

This rule needs the notated content and the rendered result together — the score says what should happen, the page says whether it did.