One of the Six Schools of traditional Hindu philosophy, Samkhya philosophy is also considered to be the oldest. Samkhya emerged before the 2nd century b.c.e., and Samkhya-type ideas have been around since at least the 6th century b.c.e, since Guatama Buddha was familiar with Samkhyan-type ideas. Proto-Samkhya speculation also appears in the Katha Upanishad (about 4th century b.c.e.), where reference is made to the following ascending sequence:
Although the school of Samkhya as such was systematized by the legendary Kapila, and the Samkhya-sutra traditionally attributed to him, in its present form it is not his original work, but dates from the 15th century.
Classical Samkhya is based on the Samkhyakarika of Ishvarakrishna, written sometime in the third to fifth century c.e. This is the earliest available Samkhya text. In Classical Samkhya, the one Conscious Spirit or Purusha is re-placed by a multiplicity of pure Consciousness souls or purushas, possibly due to Jain influence - the Jainist idea of a multiplicity of souls or jivas [Larson, Classical Samkhya, p.93]. Reality is reduced to two fundamental principles: a multiplicity of Original Subjects, passive individual centres of pure consciousness, or purushas; and a single Original Object, a non- conscious principle of unmanifest "nature" or substance, or prakriti, from which all psychic and physical realities arise.
Well-known commentaries are Gaudapada's bhasya, Vacaspati Misra's Tattwa-kaumudi, Vijnanabhiksu's Samkhya-pravacanbhasya, and Mathara's Matharavrtti. Topics traditionally emphasized by Kapila, Isvarakrishna, and later writers are the theory of causation, the metaphysical duality of conscious souls (purushas) and non-conscious nature (prakriti), the evolution of the world ou of prakriti, the concept of liberation (kaivalya), and the theory of knowledge.