The Trairūpya Puzzle: Intensional Content Beyond Formal Logic

Buddhist logicians from Dignāga onward require that a valid logical reason satisfy three modes (trairūpya): (1) the reason holds of the subject; (2) it is present wherever the probandum is present (anvaya); (3) it is absent wherever the probandum is absent (vyatireka). In first-order logic, modes (2) and (3) — ∀x(Hx → Sx) and ∀x(¬Sx → ¬Hx) — are contrapositives, i.e., logically equivalent. Yet Buddhist logicians unanimously insist both are necessary. I call this the “Trairūpya Puzzle.” After examining Oetke’s epistemic solution and Dharmakīrti’s treatment of the equivalence, I argue that the puzzle exposes a genuine limit of extensional formalization. Drawing on Dharmottara’s niyamavat doctrine and Durvekamiśra’s concept of svagata dharma — intrinsic capacities of the reason itself — I conclude that the second and third modes encode intensional content that the material conditional of first-order logic cannot capture. The trairūpya is a presentation of phenomenological relation.