Different schools consider different number of epistemic means to correct knowledge (jñāna), between one of Charvaka school to six of Advaita Vedanta: Pratyakṣa (perception), Anumāṇa (inference), Upamāṇa (comparison and analogy), Arthāpatti (postulation, derivation from circumstances), Anupalabdi (non-perception, negative/cognitive proof) and Śabda (word, testimony of past or present reliable experts).

To verify the interconnection and maps above: [1] Jeaneane Fowler (2002), Perspectives of Reality: An Introduction to the Philosophy of Hinduism, Sussex Academic Press, ISBN 978-1898723943, page 134-146; [2] Karl Potter (2004), The Encyclopedia of Indian Philosophies: Indian metaphysics and epistemology, Volume 2, Motilal Banarsidass, ISBN 978-8120803091, pages 222-238; [3] John A Grimes (2006), A Concise Dictionary of Indian Philosophy, State University of New York Press, ISBN 978-0791430675, pages 237-240