M. Cousin has called it the sensualism of India,[70] but certainly without propriety.  It is as purely ideal a doctrine as that of the Vedas.  Its two eternal principles are both ideal.  The plastic force which is one of them, Kapila distinctly declares cannot be perceived by the senses.[71] Soul, the other eternal and uncreated principle, who “is witness, solitary, bystander, spectator, and passive,"[72] is not only spiritual itself, but is clothed with a spiritual body, within the material body.  In fact, the Karika declares the material universe to be the result of the contact of the Soul with Nature, and consists in chains with which Nature binds herself, for the purpose (unconscious) of delivering the Soul.  When by a process of knowledge the Soul looks through these, and perceives the ultimate principle beyond, the material universe ceases, and both Soul and Nature are emancipated.[73]

One of the definitions of the Karika will call to mind the fourfold division of the universe by the great thinker of the ninth century, Erigena.  In his work, [Greek:  peri phuseos merismou] he asserts that there is, (1.) A Nature which creates and is not created. (2.) A Nature which is created and creates. (3.) A Nature which is created and does not create. (4.) A Nature which neither creates nor is created.  So Kapila (Karika, 3) says, “Nature, the root of all things, is productive but not a production.  Seven principles are productions and productive.  Sixteen are productions but not productive.  Soul is neither a production nor productive.”

Mr. Muir (Sanskrit Texts, Part III. p. 96) quotes the following passages in proof of the antiquity of Kapila, and the respect paid to his doctrine in very early times:—­

   Svet.  Upanishad. “The God who superintends every mode of production
   and all forms, who formerly nourished with various knowledge his son
   Kapila the rishi, and beheld him at his birth.”

   “Bhagavat Purana (I. 3, 10) makes Kapila an incarnation of Vischnu. 
   In his fifth incarnation, in the form of Kapila, he declared to Asuri
   the Sankhya which defines the collection of principles.

“Bhagavat Purana (IX. 8, 12) relates that Kapila, being attacked by the sons of King Sangara, destroyed them with fire which issued from his body.  But the author of the Purana denies that this was done in anger.  ’How could the sage, by whom the strong ship of the Sankhya was launched, on which the man seeking emancipation crosses the ocean of existence, entertain the distinction of friend and foe’?”

The Sankhya system is also frequently mentioned in the Mahabarata.

The Nyaya system differs from that of Kapila, by assuming a third eternal and indestructible principle as the basis of matter, namely, Atoms.  It also assumes the existence of a Supreme Soul, Brahma, who is almighty and allwise.  It agrees with Kapila in making all souls eternal, and distinct from body.  Its evil to be overcome is the same, namely, transmigration; and its method of release is the same, namely Buddhi, or knowledge.  It is a more dialectic system than the others, and is rather of the nature of a logic than a philosophy.