Prasthanatraya literally means the three paths towards self realization. The three canonical works – the Upanishads, Brahmasutra, and the Bhagavad Gita – form the basis of Vedanta Philosophy. They are called Shruti Prasthana, Nyaya Prasthana and Smriti Prasthana, respectively. All three taken together are termed Prasthantraya.
Upanishads – literally, the word ‘Upanishad’ means ‘to be nearby’. By extension, it means going near that place where ignorance is shattered. The principal Upanishads on which Adi Shankaracharya has written commentaries are Isha, Kena, Katha, Prashna, Mundaka, Mandukya, Chandogya, Brihadaranyaka, Aitareya and Taittiriya. Broadly speaking, their teaching is ‘Brahman’ is the only Reality and the goal of life is to realize it. The Upanishads teach that ‘Brahman’ is an all pervading Reality in relation to the world and atman is the indwelling self. Both denote the same reality, which is one without a second.
Brahmasutra – Badarayana organized and gave a coherent interpretation of the teachings of the Upanishads. His work being in a sutra form is too laconic; many commentaries have been written on it. Brahmasutra is also known as Vedanta Sutra and Sariraksutra.
Bhagavad Gita – It contains the preaching of Bhagavan Sri Krishna, given to Arjuna on the battlefield. It is in the dialogue form. It gives the harmonious blending of jnana (knowledge), bhakti (love) and karma (action) as a path for self realization. All the three paths are for cultivating Brahman consciousness.