Doubling rules by chord type and inversion

Root-position triad: double the root by default (third/fifth acceptable for smoothness); never double the leading tone or a chromatically altered tone. First-inversion triad: prefer doubling soprano's note or the bass (chordal third); never double the leading tone or chordal seventh. Second-inversion (6/4) triad: ALWAYS double the bass (chordal fifth) — firm, covering cadential/passing/pedal 6/4 alike. Diminished triad: double the THIRD, never root or fifth. Dominant/any seventh chord: never double the leading tone (third) or the seventh; if a voice must be omitted, omit the fifth before ever omitting the seventh or third.

A V7 chord voiced with the leading tone doubled between two voices — forbidden regardless of inversion.

Aldwell & Schachter — standard, near-universally taught doubling rules; outside Gould/Read/Ross/Stone's scope (harmonic content, not engraving), flagged as such.

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