A significant contribution to the history of Indian logic has been found in the archives of an old monastery in Ujjain. The manuscript, titled Yukti-Deepa-Kaustubha, dates to the 12th century and focuses entirely on the logic of counter-factual reasoning. It presents a series of sophisticated syllogisms used to establish truths by demonstrating the absurdity of their opposites, a technique known as 'tarka' taken to a high degree of formalization.
The text is particularly notable for its section on 'Hypothetical Causality,' which prefigures modern logical concepts of possible-world semantics. By analyzing 'what might have been' to prove 'what must be,' the 'Yukti-Deepa-Kaustubha' represents the pinnacle of medieval Nyaya-Vaisheshika synthesis. Experts believe this manuscript was a primary textbook for advanced logic students in the prestigious academies of ancient Ujjain.