Āstika and nāstika

Āstika and nāstika are concepts that have been used to classify the schools of Indian philosophy by modern scholars, as well as some Hindu, Buddhist and Jain texts. The various definitions for āstika and nāstika philosophies have been disputed since ancient times, and there is no consensus. One standard distinction, as within ancient- and medieval-era Sanskrit philosophical literature, is that āstika schools accept the Vedas, the ancient texts of India, as fundamentally authoritative, while the nāstika schools do not. However, a separate way of distinguishing the two terms has evolved in current Indian languages like Telugu, Hindi and Bengali, wherein āstika and its derivatives usually mean 'theist', and nāstika and its derivatives denote 'atheism'. Still, philosophical tradition maintains the earlier distinction, for example, in identifying the school of Sāṃkhya, which is non-theistic (as it does not explicitly affirm the existence of God in its classical formulation), as āstika (Veda-affirming) philosophy, though "God" is often used as an epithet for consciousness (purusha) within its doctrine. Similarly, though Buddhism is considered to be nāstika, Gautama Buddha is considered an avatar of the god Vishnu in some Hindu denominations. Due to its acceptance of the Vedas, āstika philosophy, in the original sense, is often equivalent to Hindu philosophy: philosophy that developed alongside the Hindu religion.

Āstika (Sanskrit: आस्तिक; from Sanskrit: asti, 'there is, there exists') means one who believes in the existence of a Self or Brahman, etc. It has been defined in one of three ways:

1. as those who accept the epistemic authority of the Vedas;
2. as those who accept the existence of ātman;
3. as those who accept the existence of Ishvara.

Nāstika (Sanskrit: na, 'not' + āstika), by contrast, are those who deny all the respective definitions of āstika; they do not believe in the existence of Self.

The six most studied Āstika schools of Indian philosophies, sometimes referred to as orthodox schools, are Nyāyá, Vaiśeṣika, Sāṃkhya, Yoga, Mīmāṃsā, and Vedānta. The five most studied Nāstika schools of Indian philosophies, sometimes referred to as heterodox schools, are Buddhism, Jainism, Chārvāka, Ājīvika, and Ajñana. However, 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 many are unsophisticated and flawed.