Āstika and nāstika in the context of "International Alphabet of Sanskrit Transliteration"

Hinduism (/ˈhɪnduˌɪzəm/) is an umbrella term for a range of Indian religious and spiritual traditions (sampradayas) that are unified by adherence to the concept of dharma, a cosmic order maintained by its followers through rituals and righteous living, as expounded in the Vedas. The word Hindu is an exonym, and while Hinduism has been called the oldest surviving religion in the world, it is also described by the 19th century term Sanātana Dharma (lit. 'eternal dharma'). Vaidika Dharma (lit. 'Vedic dharma') and Arya Dharma are historical endonyms for Hinduism.

Hinduism entails diverse systems of thought, marked by a range of shared concepts that discuss theology, mythology, and other topics in textual sources. Hindu texts have been classified into Śruti (lit. 'heard') and Smṛti (lit. 'remembered'). The major Hindu scriptures are the Vedas, the Upanishads, the Puranas, the Mahabharata (including the Bhagavad Gita), the Ramayana, and the Agamas. Prominent themes in Hindu beliefs include karma (action, intent and consequences), saṃsāra (the cycle of death and rebirth) and the four Puruṣārthas, proper goals or aims of human life, namely: dharma (ethics/duties), artha (prosperity/work), kama (desires/passions) and moksha (liberation/emancipation from passions and ultimately saṃsāra). Hindu religious practices include devotion (bhakti), worship (puja), sacrificial rites (yajna), and meditation (dhyana) and Yoga. Hinduism has no central doctrinal authority and many Hindus do not claim to belong to any denomination. However, scholarly studies notify four major denominations: Shaivism, Vaishnavism, Shaktism and Smartism. The six Āstika schools of Hindu philosophy that recognise the authority of the Vedas are: Sankhya, Yoga, Nyaya, Vaisheshika, Mīmāṃsā, and Vedanta.

Indian philosophy consists of philosophical traditions of the Indian subcontinent. The philosophies are often called darśana, meaning "to see" or "looking at." Ānvīkṣikī means “critical inquiry” or “investigation." Unlike darśana, ānvīkṣikī was used to refer to Indian philosophies by classical Indian philosophers, such as Chanakya in the Arthaśāstra.

A traditional Vedic classification divides āstika and nāstika schools of philosophy, depending on one of three alternate criteria: whether it believes the Vedas as a valid source of knowledge; whether the school believes in the premises of Brahman and Atman; and whether the school believes in afterlife and Devas. (though there are exceptions to the latter two: Mimamsa and Samkhya respectively).

Hindu philosophy or Vedic philosophy is the set of philosophical systems that developed in tandem with the first Hindu religious traditions during the iron and classical ages of India. In Indian philosophy, of which Hindu philosophy is a prominent subset, the word used for philosophy is Darshana (Sanskrit: दर्शन; meaning: "viewpoint or perspective"), from the Sanskrit root 'दृश' (drish) meaning 'to see, to experience'.

The schools of thought or Darshanas within Hindu philosophy largely equate to the six ancient orthodox schools: the āstika (Sanskrit: आस्तिक) schools, defined by their acceptance of the Vedas, the oldest collection of Sanskrit texts, as an authoritative source of knowledge. Of these six, Samkhya (सांख्य) is the earliest school of dualism; Yoga (योग) combines the metaphysics of Samkhya with meditation and breath techniques; Nyaya (न्याय) is a school of logic emphasising direct realism; Vaisheshika (वैषेशिक) is an offshoot of Nyaya concerned with atomism and naturalism; Mimamsa (मीमांसा) is a school justifying ritual, faith, and religious obligations; and Vedanta (वेदान्त) contains various traditions that mostly embrace nondualism.

Samkhya or Sankhya (/ˈsɑːŋkjə/; Sanskrit: सांख्य, romanized: Sāṅkhya) is a dualistic orthodox school of Hindu philosophy. It views reality as composed of two independent principles, Puruṣa ('consciousness' or spirit) and Prakṛti (nature or matter, including the human mind and emotions).

Puruṣa is the witness-consciousness. It is absolute, independent, free, beyond perception, above any experience by mind or senses, and impossible to describe in words.

Mīmāṁsā (Sanskrit: मीमांसा; IAST: Mīmāṁsā) is a Sanskrit word that means "reflection" or "critical investigation" and thus refers to a tradition of contemplation which reflected on the meanings of certain Vedic texts. This tradition is also known as Pūrva-Mīmāṁsā because of its focus on the earlier (pūrva) Vedic texts dealing with ritual actions, and similarly as Karma-Mīmāṁsā due to its focus on ritual action (karma). It is one of six Vedic "affirming" (āstika) schools of Hindu philosophy. This particular school is known for its philosophical theories on the nature of Dharma, based on hermeneutics of the Vedas, especially the Brāḥmanas and samhitas. The Mīmāṃsā school was foundational and influential for the Vedāntic schools, which were also known as Uttara-Mīmāṁsā for their focus on the "later" (uttara) portions of the Vedas, the Upanishads. While both "earlier" and "later" Mīmāṁsā investigate the aim of human action, they do so with different attitudes towards the necessity of ritual praxis.

Mīmāṁsā has several sub-schools, each defined by its pramana. The Prabhākara sub-school, which takes its name from the seventh-century philosopher Prabhākara, described the five epistemically reliable means to gaining knowledge: pratyakṣa or perception; anumāna or inference; upamāṇa, comparison and analogy; arthāpatti, the use of postulation and derivation from circumstances; and shabda, the word or testimony of past or present reliable experts. The Bhāṭṭa sub-school, from philosopher Kumārila Bhaṭṭa, added a sixth means to its canon; anupalabdhi meant non-perception, or proof by the absence of cognition (e.g., the lack of gunpowder on a suspect's hand)

Vedanta (/veɪˈdɑːntə/; Sanskrit: वेदान्त, IAST: Vedānta [ʋeːdɑ́ːntɐ]), also known as Uttara Mīmāṃsā, is one of the six orthodox (āstika) traditions of Hindu philosophy and textual exegesis. The word Vedanta means 'conclusion of the Vedas,' and encompasses the ideas that emerged from, or aligned and reinterpreted, the speculations and enumerations contained in the Upanishads, focusing, with varying emphasis, on devotion, knowledge, and liberation. Vedanta developed into many traditions, all of which give their specific interpretations of a common group of texts called the Prasthānatrayī, translated as 'the three sources': the Upanishads, the Brahma Sutras, and the Bhagavad Gita.

All Vedanta traditions place great emphasis on textual exegesis and contain extensive discussions on ontology, soteriology, and epistemology, even as there is much disagreement among the various traditions. Independently considered, they may seem completely disparate due to the pronounced differences in thoughts and reasoning.

Ajivika (Sanskrit: आजीविक, IAST: Ājīvika) is an ancient nāstika, or 'heterodox,' Indian school of absolute fatalism or extreme determinism. The Ājīvika school is known for its Niyati ("Fate") doctrine and for the premise that there is no free will, that everything that has happened, is happening and will happen is entirely preordained and a function of cosmic principles.

Believed to have been founded in the 5th century BCE by Makkhali Gosāla, it was a Śramaṇa movement and a major rival to other contemporary orthodox and heterodox movements within the Indian philosophical milieu. Ājīvikas were organized renunciates who formed discrete communities. The precise identity of the Ājīvikas is not well known, and it is even unclear if they were a divergent sect of the Buddhists or the Jains.

Ajñāna (Sanskrit: अज्ञान, (Vedic) IPA: /ɐd͡ʑ.ɲɑː.nɐ/; (Classical) IPA: /ɐd͡ʑˈɲɑː.n̪ɐ/) is an ancient nāstika, or 'heterodox,' Indian school of agnosticism that embraces radical skepticism. It emerged as a Śramaṇa movement and was a major rival of early Buddhism, Jainism and the Ājīvika school. They have been recorded in Buddhist and Jain texts. They held that it was impossible to obtain knowledge of metaphysical nature or ascertain the truth value of philosophical propositions; and even if knowledge was possible, it was useless and disadvantageous for final salvation. They specialized in refutation without propagating any positive doctrine of their own. Sanjaya Belatthiputta was one of the major proponents of this school of thought.