Indian philosophies mean generally the Sada Darsana or the six different schools of philosophers namely, 1. the Mimamsa, 2. Sankhya, 3. Nyaya, 4. Mayavada, 5. Patanjal and 6. the Vedanta. The last named Vedanta Darsana was compiled by Sri Vyasa after a thorough refutation of all other five Darsanas and therefore Vedanta is accepted by all Indian scholars and no body is recognized as bona fide who has no interpretation of this Vedanta Darsana.
The Western philosophers mostly of the Sankhya school have less aquaintance with the Vedanta Darsana and philosophers like Kant, Mill, Aristotle or Schopenhauer etc all belong to either of the above five Darsanas except Vedanta because limited human thinking power cannot go beyond that stage. But Vedanta Darsana is far beyond the limited mental speculation of the human brain conditioned by material nature.
Letter to Mr. Bailey, 2 October, 1951