The Brahma Sutras (brahma sūtrāṇi) by the author Bādarāyaṇa is a condensed, concise text for advanced students, which has several functions. It aims to represent the teaching aphoristically in its complexity and completeness. But it also places other points of view (darśanas) in the non-dual panorama of reality. The Vedantin knows this phenomenon, because as his knowledge greets, he recognizes the level at which all kinds of contemporary spiritual teachings are. This is universal and timeless, and no different from Indian Antiquity.

Although the brahma sutras are essentially uttara mīmāṃsā (supreme logic) themselves, they use techniques from purva mīmāṃsā (previous, premature) logic. These are in particular:

1. Viṣaya The subject (e.g., a Vedic statement)
2. Saṃśaya The doubt or question (what does it mean?)
3. Pūrvapakṣa A possible opposition or alternative point of view
4. Siddhānta The final, reasoned position
5. Saṅgati The connection with preceding or following sūtras

The joke is that the brahma sutras is actually a non-dual text, which reconciles the other texts with itself, by giving them a place in the true non-dual vision of advaita vedānta.

Yet, in addition to Śaṅkara, who of course emphasized that only jñāna (knowledge) is the direct means of mokṣa, Rāmānuja (Viśiṣṭādvaita, qualified non-duality) and Madhva (Dvaita, duality) have also written commentaries (bhāṣya) on the brahma sutras. This is something curious, because the brahhma sutras themselves explain what is wrong with their teaching.

The other two sources of vedānta are śruti- and smṛti prasthāna. Śruti means that which has been heard, in the sense of “echoes in the minds of mature seers”. These are the vedas with the upaniṣads within them. Śruti is the real source, and does not come from humans (apauruṣeya).

Smṛti is the complete teaching, as remembered by a human being, Vyāsa in this case, in a form that is cast in a human being. That is what the Bhagavad Gītā has produced. A text that teaches a person how to live in order to be free from man and his life. Freedom of the jīva, and then apparently a free life for the jīva.

Another word for reason (nyāya) is tarka.