Nagarjuna (c. 150 – c. 250 CE), one of the most influential Buddhist thinkers, defended the theory of the emptiness (shunyata) of phenomena and attacked theories that posited an essence or true existence (svabhava) to phenomena in his magnum opus The Fundamental Verses on the Middle Way. He used the Buddhist catuṣkoṭi ("four corners" or "four positions") to construct reductio ad absurdum arguments against numerous theories which posited essences to certain phenomena, such as causality and movement. In Nagarjuna's works and those of his followers, the four positions on a particular thesis are negated or ruled out (Sk. "pratiṣedha") as exemplified by the first verse of Nagarjuna's Middle way verses which focuses on a critique of causation: