One of the six Hindu ‘orthodox’ philosophies (darshanas), Samkhya is also the oldest, being attributed to the sage Kapila (c.7th c. bc). Its metaphysics is based upon a subtle analysis of causation, whereby effects are seen as pre-existent in their causes (both this doctrine, satkaryavada, and its denial, asatkaryavada, are criticized by the Vedanta school, as well as by Buddhism, in favour of a Parmenidean rejection of change altogether). Samkhya criticizes the concept of causation as a regular succession of events, or indeed as any relation between distinct events or states of affairs, promoting instead a concept of the unfolding of the cosmos as a unified single process, in which each state is already pregnant with those that are to come. It recognizes two realities, the purusha whose essence is consciousness, and praktri, the eternal, unconscious, unchanging principle that is the cause of the world. The real self is separate from the body, but suffering is caused by lack of discrimination between the real self and the non-self. This failure can be overcome by a long training in Yoga and meditation upon the eternal and transcendental nature of the true self.