Āstika and nāstika

Āstika (Sanskrit: आस्तिक, IAST: āstika) and nāstika (Sanskrit: नास्तिक, IAST: nāstika) are mutually exclusive terms that modern scholars use to classify the schools of Indian philosophy 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:

Nāstika (Sanskrit: नास्तिक; from 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.

Āstika is a Sanskrit adjective and noun that derives from asti ('there is or exists'), meaning 'knowing that which exists' or 'pious.' The word Nāstika (na, not, + āstika) is its negative.

One of the traditional etymologies of the term āstika—based on Pāṇini's Aṣṭādhyāyī 4.4.60 ("astināstidiṣṭam matiḥ")—defines the concept as 'he whose opinion is that Īśvara exists' (asti īśvara iti matir yasya). According to Sanskrit grammarian Hemachandra, āstika is a synonym for 'he who believes'. Other definitions include:

As used in Hindu philosophy, the differentiation between āstika and nāstika does not refer to theism or atheism. The terms often, but not always, relate to accepting Vedic literature as an authority, particularly on their teachings on Self. The Veda and Hinduism do not subscribe to or include the concept of an almighty that is separate from oneself i.e. there is no concept of God in the Christian or Islamic sense. N. N. Bhattacharya writes: