As per Āstika tradition of Hinduism, there are four authorized epistemic authorities termed as Pramāṇas Śāstras. They are the sources of reference for Puruṣārtha (dharma, Artha, Kāma and Mokṣa), the laws of the universe and of human conduct (Ācāra). It is considered obligatory to get accord from these epistemic sources, i.e. to have Śāstra pramāṇaṃ^[1]. They are specified in an order as śruti (Vedas); smṛti, "that which is remembered, tradition (Dharmaśāstra); ācāra, good custom; and ātmatuṣṭi, "what is pleasing to oneself."^[2] The first two are undisputed epistemic sources (pramāṇa), where śruti holds the ultimate or supreme authority as Śāstra pramāṇam. However, there is difference of opinion for the rest of the epistemicauthorized sources.

The importance of Śāstra pramāṇam in Hinduism can be understood from Bhagavadgita (Chapter 16, verse 24), where it is commanded by Krishna to have Śāstra pramāṇam before ascertaining what is to be done.^{[3][4][note 1]}

According to Bhavishya Purana, Brahmaparva, Adhyaya 7, there are four sources of dharma: Śruti (Vedas), Smṛti (Dharmaśāstras, Puranas), Śiṣṭa Āchāra/Sadāchara (conduct of noble people) and finally Ātma tuṣṭi (self satisfaction). From the sloka:

वेदः स्मृतिः सदाचारः स्वस्य च प्रियमात्मनः । एतच्चतुर्विधं प्राहुः साक्षाद्धर्मस्य लक्षणम् ॥^[6]

vedaḥ smṛtiḥ sadācāraḥ svasya ca priyamātmanaḥ
etaccaturvidhaṃ prāhuḥ sākshāddharmasya lakshaṇam

– Bhavishya Purāṇa, Brahmaparva, Adhyāya 7

The meaning is: "vedas, smritis, good (approved) tradition and what is agreeable to one's soul (conscience), the wise have declared to be the four direct evidences of dharma."

Shruti (Sanskrit: श्रुति, IAST: Śruti, IPA: [ɕɽʊtɪ]) is considered as the ultimate epistemic authority or prathama pramāṇa. Shruti in Sanskrit means "that which is heard" and refers to the body of most authoritative, ancient religious texts comprising the central canon of Hinduism.^[7] Manusmriti states that Śrutistu vedo vigneyaḥ (Sanskrit: श्रुतिस्तु वेदो विज्ञेय:, lit. means "Know that Vedas are Śruti"). Thus, it includes the four Vedas including its four types of embedded texts—the Samhitas, the early Upanishads, the Brahmanas and the Aranyakas.^[8][9]

Smriti (Sanskrit: स्मृति, IAST: Smṛti) is considered as the penultimate epistemic authority or dvitīya pramāṇa. Smriti literally means "that which is remembered" and it a body of Hindu texts usually attributed to an author, traditionally written down, in contrast to Śrutis (the Vedic literature) considered authorless, that were transmitted verbally across the generations and fixed.^[8] Smriti is a derivative secondary work and is considered less authoritative than Sruti in Hinduism, except in the Mimamsa school of Hindu philosophy.^[7][10][11] The authority of smriti accepted by orthodox schools, is derived from that of shruti, on which it is based.^[12][13]

The Smrti literature is a corpus of diverse varied texts.^[7] This corpus includes, but is not limited to the six Vedāngas (the auxiliary sciences in the Vedas), the epics (the Mahābhārata and Rāmāyana), the Dharmasūtras and Dharmaśāstras (or Smritiśāstras), the Arthasaśāstras, the Purānas, the Kāvya or poetical literature, extensive Bhasyas (reviews and commentaries on Shrutis and non-Shruti texts), and numerous Nibandhas (digests) covering politics, ethics (Nitisastras),^[14] culture, arts and society.^[15][16]

Each Smriti text exists in many versions, with many different readings.^[8] Smritis were considered fluid and freely rewritten by anyone in ancient and medieval Hindu tradition.^[8][10]

While is unanimous opinion among sages on the ultimate and penultimate epistemic authority, there is some difference of opinion what constitute as antepenultimate one or tṛtīya pramāṇa. This has been clearly pointed out during the times of Mahabharata itself. In Anuśāsana-parva of Mahabharata, it is mentioned as

धर्मं जिज्ञासमानानां प्रमाणं प्रथमं श्रुतिः । द्वितीयं धर्मशास्त्रं तु तृतीयो लोकसंग्रहः​ ॥

dharmaṃ jijñāsamānānāṃ pramāṇaṃ prathamaṃ śrutiḥ
dvitīyaṃ dharmaśāstraṃ tu tṛtīyo lokasangrahaḥ

– Mahābhāratam, Anuśāsana-parvam

The meaning is those who have the 'desire to know dharma' (dharma jijñāsa), the first pramāṇa is śruti. The second pramāṇa are the dharmaśāstras (i.e. the dharma part of smṛti). The third reference is as per the custom of the people.

To Manu, Yājñavalkya, Vaśiṣṭha and Baudhayana, the virtuous conduct of Śiṣṭas (virtous learned men) and practice of good men, Sadāchara is the antepenultimate pramāṇa after Śrutis and Smṛtis. ^[17]. Vaśiṣṭhasmṛti verse 1.4 quotes, tadalabhe śiṣṭāchārah pramāṇam, i.e. only if the relevant referenes are absent in those both, then Śiṣṭa Āchāra can be considered as Antepenultimate pramāṇa. According to the sage Vaśiṣṭha, Śruti and Smṛti are more important sources than others.^[18] The Padma Purana also prescribes as similar view.^{[note 2]}

Ācāra (Sanskrit: आचार) is a concept used in the context of Classical Hindu law that refers to the customary laws or community norms of a particular social group.^[20] These community norms are delineated and put into practice by people who have earned the respect of those within each individual group, such as a community leader or elder. Although in Dharmaśāstra the ideal person who defines the ācāra of a particular place is dictated as one who knows the Vedas or is “learned”, in actual practice this role is often deferred to group leaders along with Vedic scholars.^[21] Ācāra is theologically important in Hindu law because it is considered, along with the Vedas (Śruti), and Smriti (traditional texts such as the Dharmaśāstra literature), to be one of the sources of dharma.^[22] Particular regional ācāra is believed to be canonized in Dharmaśāstra texts; however scholars differ on the source for the actual accounts found within these texts.^[23]

However, Āpastamba considers purāṇa as antepenultimate source of reference. In his Āpastambasmṛti, it has been mentioned as

यददृष्टम् हि वेदेषु तत् द्रष्टव्यं स्मृतौ किल​ । उभाभ्यां यददृष्टस्तु तत् पुराणेषु पठ्यते ॥^{[note 3]}

yat adṛṣṭam hi vedeṣu tat draṣṭavyaṃ smṛta kila
ubhābhyāṃ yat adṛṣṭastu tat purāṇeṣu paṭhyate

– Āpastambasmṛti

The meaning is whenever there is no reference in vedas then smṛtis are to be referred. In case references are absent in the both, then purāṇas are to be consulted.

Atmatusti is usually translated into English as being "what is pleasing to oneself."^[25] The first three sources of law are rooted in the vedas, whereas atmatusti is not. It is because of this that atmatusti, as a fourth source (i.e. caturtha pramāṇa), is not recognized by most scholars due to the lack of legitimacy. Only Manu and Yājñavalkya refer to atmatusti as the fourth source of dharma within the Hindu Law tradition. Textual accounts of Manu's and Yajnavalkya's placement of atmatusti as a fourth source of dharma can be found in The Law Code of Manu 2.6 and The Law Code of Yajnavalkya 1.7. Also, atmatusti does not share the same authority as sruti, smriti, and acara. Atmatusti differs significantly from the other three sources of dharma in that it is not based on an "authority exterior to man"; in other words, an individual is able to create their own authority for any issue not covered under sruti, smriti, and acara.^[26]

Ātmatuṣṭi is also known as Hṛdayānujña (free will) is mentioned also by Manu, Yājñavalkya and Vishnu distinctly mention this as a or source of moral and religion knowledge^[27]. Yājñavalkya goes further step adding good intent as additional fifth source of Dharma.^{[note 4]}

Conflict between different epistemic sources, generally termed as virodha. When there is an instance of conflict between the smriti and the śruti, the śruti shall prevail.^{[30][note 5]} Similarly, Whenever there is conflict between different epistemic sources in general, then as per Āpastamba, it is advised to refer more preceding epistemic sources as they hold more authority. In Āpastambasmṛti, it is mentioned as

श्रुतिस्मृतिपुराणेषु विरुद्धेषु परस्परम् । पूर्वं पूर्वं बलीयं स्यादिति न्यायविदो विदुः ॥

śrutismṛtipurāṇeṣu viruddheṣu parasparam
pūrvaṃ pūrvaṃ balīyam syāditi nyāyavido viduḥ

– Āpastambasmṛti

The meaning is whenever there is mutual conflict between vedas, smṛtis and purāṇas, then the ones well-versed in nyāya suggest that more preceding epistemic source holds higher weightage (than the later epistemic one).

• Pramāṇa
• Prasthanatrayi
• Āstika and nāstika
• Dharma (Buddhism)

• Domenico Francavilla (2006), The roots of hindu jurisprudence: sources of Dharma and interpretation in Mīmāṃsā and Dharmaśāstra

• Schools of Jurisprudence – Concept of Dharma