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The system of Prasthantrayi (samskrit:प्रस्थानत्रयी) is a hermeneutic for understanding the import of vedanta and of vedas established by Sripad Adi Shankaracharya .
There are six systems of philosophy known as sad-dharsanas. They accept the vedas as authority but they have different interpretations of what the vedas mean. Shankaracharya established that vedanta is the conclusion of the vedas (gives actual conclusive import of the vedas). But then what is the import of vedanta ? There can be different opinions about this also.
Now which books to quote to prove a point. That is primary canon. To resolve this, Sripad Adi Shankaracharya came up with this system.
The Three Prasthanas
S Radhakrishnan writes the following:
"The three Prasthanas or divisions of Vedanata are: The Upanishads, Brahma Sutra and the Bhagavad Gita. The three Prasthanas answer roughly to three stages of faith, knowledge and discipline. The Upanishads embody the experience of the sages. Logic and discipline are present in them though these are not the chief characteristics of those texts. The Brahma Sutra attempts to interpret in logical terms, the chief conclusions of the Upanishads. The Bhagavad Gita is primarily a Yoga Sastra giving us the chief means by which we can attain the truly religious life. These three form together the absolute standard of the Hindu tradition".
Pandey & Navare (2018) mention: Hindu tradition acknowledges the Prasthānatrayī as its three primary sources. The texts comprising the Prasthānatrayī are the Upaniṣada , the Bhagavad-Gītā, and the Brahmasūtra.
The system (that particular structure) of Prasthan trayi was accepted by subsequent acharyas also. Sripad Madhvacharya, Sripad Ramanujacharya, Sripad Baladev Vidyabhushan and others have all commented on this Prasthan trayi and thats how they established the authenticity of their sampradayas.
- Radhakrishnan, S. (1926). Hindu view of life. George Allen And Unwin Ltd, London.
- Pandey, A., & Navare, A. V. (2018). Paths of Yoga: Perspective for Workplace Spirituality. In The Palgrave Handbook of Workplace Spirituality and Fulfilment. Palgrave Macmillan Cham.