Dr.Weber at one time was of the opinion that Kapila and Buddha were the same person, but afterward retracted this opinion.[57] Colebrooke says that Kapila is mentioned in the Veda itself, but intimates that this is probably another sage of the same name.[58] The sage was even considered to be an incarnation of Vischnu, or of Agni.

The Vedanta philosophy is also said by Lassen to be mentioned in the Laws of Manu.[59] This system is founded on the Upanishads, and would seem to be later than that of Kapila, since it criticises his system, and devotes much space to its confutation.[60] But Duncker regards it as the oldest, and already beginning in the Upanishads of the Vedas.[61] As the oldest works now extant in both systems are later than their origin, this question of date can only be determined from their contents.

That which logically precedes the other must be chronologically the oldest.
The Sankhya system of Kapila is contained in many works, but notably in the Karika, or Sankhya-Karika, by Iswara Krishna.

This consists in eighty-two memorial verses, with a commentary.[62] The Vedanta is contained in the Sutras, the Upanishads, and especially the Brahma-Sutra attributed to Vyasa.[63] The Nyaya is to be found in the Sutras of Gotama and Canade.[64] These three systems of Hindoo philosophy, the Sankhya, the Nyaya, and the Vedanta, reach far back into a misty twilight, which leaves it doubtful when they began or who were their real authors.

In some points they agree, in others they are widely opposed.