Samkhya means to enumerate, analyse or count and it is a school of Hindu philosophy founded by sage Kapila. It deals with the analysis and discernment of the different properties of consciousness and matter([wiki]purusha[/wiki] and [wiki]prakriti[/wiki]) and their interactions with one another.

Samkhya philosophy underpins Yoga philosophy and practice entirely. It is also the foundation of Ayurveda and much of Hinduism and is considered by scholars to be amongst the oldest philosophies in the world(if not the oldest itself). It can be traced in a rudimentary form to the [wiki]Vedas[/wiki]. Later, it is found in a more developed form in the [I]Bhagvad Gita[/I] which contains a chapter on Samkhya. The former are considered to be theistic forms of Samkhya, later a formal and atheistic school of Samkhya develops. The [I]Samkhyakarika [/I]by Isvarkrishna is the oldest extant text of the formal school. The Samkhyakarika is a philosophical/metaphysical treatise which explains using rigorous logic the Samkhya theories of physics, cosmology and psychology.

Most of the well known concepts in Yoga philosophy and much of the Yogic vocabulary comes from Samkhya theories. For example the concept of yugas or cycles of time, karma, reincarnation and spiritual evolution comes from the Samkhya theory of cosmology; the apparatus of the mind-body consisting of 5 senses(jnanaindriyas), 5 motor organs(karmaindriyas), 5 subtle elements(tanmatras), 5 material elements(mahabhuttas), mind(manas), false ego(ahamkara), intellect(buddhi) and subtle body comes from Samkhya theory of psychology. The concepts of prakriti or original matter, and the gunas or fundamental forces within matter, the 5 pranas or 5 vital life forces, comes from Samkhya theories of physics. In short Samkhya is beating at the very heart of Yoga. Indeed, it is the master system behind Yoga.

This article is fairly accurate, except that it contains a little of what I like to call Hindu spin. Hindu’s like to claim Samkhya as their own, but the Samkhya philosophy of Kapila contains many concepts that Hindus do not accept, so the Samkhya of Kapila cannot be called Hindu.

Surya Deva claims that the Samkhya Karika is the oldest extant text of the Samkhya school, but Surya Deva does not know that the text of the Samkhya Karika is extant. In fact, the Karika itself refers to an older text, and states that it is an abridgment of that earlier text, and even names the chapters that it omits. There is another work, known as the Samkhya Pravachana Sutram, that predates both the Samkhya Karika and the Bhagavad Gita. This text contains the full explanation of the Samkhya philosophy, and includes the chapters that were omitted from the Karika. Hindus, however, do not acknowledge this text.