Suresvarācārya (9th century), one of the main representatives of the Indian school of Non-Duality (Advaita Vedānta), undertakes, in chapter 3 of his work Naiṣkarmyasiddhi, a systematic reflection on the mahāvākyas - “great sentences” of the Upaniṣads that declare the ontological non-difference between the essentiality of the subject (ātman) and the essentiality of reality in totum (Brahman). In a context of fidelity to a tradition of debates with a commitment to the Truth (vāda/saṁvāda), Suresvarācārya faces wholeheartedly three fundamental aporias: (i) how to attain the knowledge of an unobjectifiable principle, inaccessible to the substantiating functionality of reasoning?; (ii) how to attain the knowledge of that same principle by resorting to traditional means of knowledge (pramāṇa), subsumed by the assumption of objectification?; (iii) how to sustain, in line with the postulates of the school of Non-Duality, that traditional authority (śruti-śabdha), one of those means of knowledge, can play a decisive role in the knowledge of that unobjectifiable principle? To address those queries, Suresvarācārya states that traditional authority is the proponent of an extra-ordinary form of reasoning (vicāra), whose modus operandi involves an equally extra-ordinary instrumentalization of the other means of knowledge, especially the (logic of) negation (abhāva/anupalabdhi/niṣedha). More specifically, this extra-ordinary functionality of reasoning puts forward a process of systematic negation, described by Suresvarācārya as “negation of negation”, abounding in propositive, existential and soteriological implications.