Source

प्रस्थान-त्रय

Prasthaana-traya are the three text sources from which vedanta arises.

The the key scriptural writings are known as the Veda-s. These are four in number; Rg, Saama, Yajur and Atharva. Within the mantras lie all the instructions of how to live.  Each veda is divided into 'actions' and 'knowledge' portions (कर्म-काण्ड /karma-kaanda and ज्ञान-काण्ड /jnaana-kaanda). 

The extraction of all the knowledge, discussions on its meaning, methodology of enquiry and so on appears in this philosophical section, which are individually referred to as The Upanishads. These are the foundation of vedanta.

उपनिषद /Upa = close/near; nishadt(nn) = seated. To sit close by.  This is traditionally used in relation to students sitting close by guru, who would recite the mantras and they would memorise them in turn, along with the meanings and implications.  The students were expected to mull over these lessons, test them, apply them, experiment with them and seek to find the proof in them. There over 100 upanishads and whilst all lead to the same conclusion, they are of differing levels of 'difficulty' for the mind to tackle.

This rigorous intellectual process is what makes this a highly scientific philosophy.  It is solidly based in logic and practices have been proved repeatedly for centuries.  Adhering to the parameters laid down, it is said, one cannot fail to experience the truth in the teachings.

Another major text in the triad are the Brahma-Sutras (भ्रम-सूत्राः). These are 'narrations' of the upanishads, an attempt to clarify them through further versification.  The third major text is the भगवद्गीता /Bhagavad Gita. 

Further to these are writings of Sri Adi Shankaraachaarya, who gave us many expositions on these works, called as भाष्य /bhaashya; his authority is recognised and homage paid by thus referring to this master as Bhaashya-kaara.  Additional texts are also utilised, but essentially all else are expositions and interpretations of the existing texts.

Hari Om