Samkhya is the oldest of the Aastika or Orthodox philosophical systems in Hinduism. Samkhya means Enumeration. The founder of the Sankya school of Philosophy was Maharishi Kapil.
The Samkya School believes in Dualism and says that there are only two realities viz. Purusha and Prakriti. While Purusha is eternal, pure consciousness, Prakriti is substance or realm of matter. Prakriti consists of varying levels of three dispositions or categories of qualities viz. Activity (rajas), Inactivity (tamas) and Harmony (sattva). An imbalance in the intertwined relationship of these three dispositions causes the world to evolve from Prakriti. This evolution from Prakriti causes the creation of 23 constituents, including intellect (buddhi), ego (ahamkara) and mind (manas).
As per this school, life or Jiva is a state in which puruṣa is bonded to prakriti through the glue of desire, and the end of this bondage is moksha. Thus, the Samkhya school does not believe in existance of God but only two realities Purush and Prakriti. However, it does not describe what happens after moksha and does not mention anything about God, because after liberation there is no essential distinction of individual and universal puruṣa. Thus, what happens after Moksha is irrelevant thing for this school. However, despite not believing in God, the Samkhya school believed in Doctrine of Karma and transmigration of souls. It also believes in existance of many living souls (Jeevatmas) who possess consciousness. It says that Puruṣa, the eternal pure consciousness, due to ignorance, identifies itself with products of Prakriti such as intellect (buddhi) and ego (ahamkara). This results in endless transmigration and suffering. However, once the realization arises that Puruṣa is distinct from Prakriti, the Self is no longer subject to transmigration and absolute freedom arises.
Difference between Dualism of Samkhya and Dualism of West
In Samkhya School of philosophy, the dualism consists of fundamental difference between consciousness and matter. It is different from the dualism in west, because in that the dualism differentiates between mind and body.
The Sankhya system of philosophy lost ground in the Gupta period because its theism was absorbed by the epics and its categories of Prakrti, Purusa and Gunas were taken over by Vedanta.