Āstika and nāstika

Āstika ("there is, there exists") and nāstika ("not āstika") are concepts used by the Brahmanical tradition, and modern scholars to classify and contrast Indian philosophies. Āstika has been defined in one of three ways; as those who accept the epistemic authority of the Vedas, as those who accept the existence of ātman, or as those who accept the existence of Ishvara. In contrast, nāstika are those who deny the respective foundational definitions of āstika.

The various definitions for āstika and nastika philosophies has been disputed since ancient times, and there is no consensus.Buddhism is considered to be nāstika, but the Gautama Buddha is considered an avatar of Vishnu in some Hindu traditions. The most studied Āstika schools of Indian philosophies, sometimes referred to as orthodox schools, are six: Nyāyá, Vaiśeṣika, Sāṃkhya, Yoga, Mīmāṃsā, and Vedānta – all schools of Hinduism. The most studied Nāstika schools of Indian philosophies, sometimes referred to as heterodox schools, are four: Buddhism, Jainism, Cārvāka, and Ājīvika – last two are also schools of Hinduism. This orthodox-heterodox terminology is a construct of Western languages, and lacks scholarly roots in Sanskrit. Recent scholarly studies state that there have been various heresiological translations of Āstika and Nāstika in 20th century literature on Indian philosophies, but quite many are unsophisticated and flawed.