Astika (Sanskrit: आस्तिक: "orthodox") and Nastika: ("heterodox") are technical terms in Hinduism used to classify philosophical schools and persons, according to whether they accept the authority of the Vedas as supreme revealed scriptures, or not. By this definition, Nyaya, Vaisheshika, Samkhya, Yoga, Purva Mimamsa and Vedanta are classified as astika schools; while Charvaka, Jainism and Buddhism are considered nastika schools.
In non-technical usage, the term astika is sometimes loosely translated as "theist" while nastika is translated as "atheist". However this interpretation is distinct from the use of the term in Hindu philosophy. Notably even among the astika schools, samkhya and the early mimamsa school do not accept a God (see Atheism in Hinduism) while accepting the authority of the Vedas; they thus are "atheistic astika schools".
The three main heterodox schools of Indian philosophy do not base their beliefs on Vedic authority:
The use of the term nastika to describe Buddhism and Jainism in India is explained by Gavin Flood as follows:
At an early period, during the formation of the Upanişads and the rise of Buddhism and Jainism, we must envisage a common heritage of meditation and mental discipline practiced by renouncers with varying affiliations to non-orthodox (Veda-rejecting) and orthodox (Veda-accepting) traditions.... These schools [such as Buddhism and Jainism] are understandably regarded as heterodox (nāstika) by orthodox (āstika) Brahmanism.
The Tantric traditions in Hinduism, have both astika and nastika lines; as Banerji writes in "Tantra in Bengal":
Tantras are ... also divided as āstika or Vedic and nāstika or non-Vedic. In accordance with the predominance of the deity the āstika works are again divided as Śākta, Śaiva, Saura, Gāṇapatya and Vaiṣṇava.
- pp. 82, 224-49. Flood, Gavin (1996). An Introduction to Hinduism. Cambridge: Cambridge University Press.
- For an overview of this method of classification, with detail on the grouping of schools, see: Radhakrishnan, Sarvepalli; and Moore, Charles A. A Source Book in Indian Philosophy. Princeton University Press; 1957. Princeton paperback 12th edition, 1989. ISBN 0-691-01958-4.
- For instance, the "Atheist Society of India" produces a monthly publications Nasthika Yugam which it translates as "The Age of Atheism".
- "By Sāṃkhya reasoning, the material principle itself simply evolves into complex forms, and there is no need to hold that some spiritual power governs the material principle or its ultimate source." Francis Clooney, CJ, "Restoring 'Hindu Theology' as a category in Indian intellectual discourse", in "Blackwell companion to Hinduism", Flood, Gavin (Ed.) Blackwell Publishing, 2003. ISBN 0-631-21535-2
- Flood, op. cit., p. 82.
- Banerji, S. C. Tantra in Bengal. Second Revised and Enlarged Edition. (Manohar: Delhi, 1992) ISBN 81-85425-63-9.
- Flood, Gavin (1996). An Introduction to Hinduism. Cambridge: Cambridge University Press.
- Flood, Gavin (Ed.), "Blackwell companion to Hinduism", Blackwell Publishing, 2003. ISBN 0-631-21535-2
- Radhakrishnan, Sarvepalli; and Moore, Charles A. A Source Book in Indian Philosophy. Princeton University Press; 1957. Princeton paperback 12th edition, 1989. ISBN 0-691-01958-4.