The six darSanas are schools of thought which explain the essential content of the Vedas by intellectual reasoning. They are at the extreme end of the spectrum of secondary scriptures. They are, with names of the first propagators :
Each darSana (= facet or viewpoint) owes its origin to a collection of aphorisms (= sUtras) . It emphasizes a certain aspect of the vedas as its dominant theme. The yoga-darSana makes the theme of mystic experimentation the dominant factor. The pUrva-mImAmsa darSana emphasizes the karma kANDa of the vedas as the dominant theme and purpose of life.
At different times in the past history of India, different darSanas have held their sway. Contemporary opinion holds that it is the vedAnta-darSana of Badarayana (identified with Vyasa by orthodox opinion) that is suited to the modern age of scientific enquiry. Though there are so many scriptures the Vedanta school relies heavily on three only:
The Upanishads (from the Sruti)
The bhagavad-gItA (from the smRti)
The brahma-sUtras (vedAnta-darSana)
These three are collectively known as the prasthAna-traya. Major religious teachers have written elaborate commentaries on these. The three schools of Vedanta with which the three major Masters -- Sankara, Ramanuja and Madhwa -- are identified, have been sustained to this day by successive generations of AcAryas(Masters) who have held the torch of that school of thought and have contributed enormously to the propagation of that thought. As a result of the influence of this succession of AcAryas, the Vedanta-darSana has become so much a part of scholarly Hinduism that the word Vedanta itself has come to mean 'philosophy' in Indian languages.