Nagarjuna's Dialectical Method and Tetralemma

The catuskoti, or tetralemma ("four corners"), is a distinctive logical structure inherited by Nagarjuna from earlier Indian philosophical and specifically Buddhist tradition — instances of fourfold analysis of a proposition already appear in the Pali Canon's treatment of questions the Buddha famously declined to answer, the so-called "undetermined questions" (avyakata) concerning, for instance, whether the world is eternal or not, whether it is finite or not, and whether the enlightened one exists, does not exist, both, or neither after death. Rather than adopting this fourfold structure merely as an inherited rhetorical convention, however, Nagarjuna deploys it as a rigorous philosophical instrument, systematically working through and rejecting all four possible positions — affirmation, negation, both, and neither — regarding some proposed inherently existing entity or process, in order to demonstrate that the entire fourfold logical space collapses once the presupposition of inherent existence (svabhava) underlying all four options is itself removed.