Prasthana Trayi (प्रस्थानत्रयी)
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 foundations
Sripad Adi Shankaracharya's has the credit for the systematization of the Vedic literatures and Vedic tradition at large. He united the broad Vedic tradition and systematized it.
Shruti , Smriti and Nyaya are the primary books through which the import of the vedanta can be understood which in turn give the import of the vedas.
1. Shruti - Vedas, Upanisads
2. Smriti - Puranas, Itihasas
3. Nyaya - Vedanta Sutra
They are called the Prasthan trayi - 'three foundations'
Unanimous acceptance
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.