The Samkhya and Yoga are two of the oldest metaphysical and soteriological systems of the Hindu tradition—their classical versions were developed between 2400 and 3000 years ago. Both systems are practical in their motivations, in the sense that they do not seek truth as an end in itself but as a means of liberation and fulfillment. They seek release from suffering which is the general condition of human existence—the suffering, they hold, is the result of metaphysical ignorance, lack of self-discipline, and adverse material conditions. The essential difference between them is that in Samkhya, the emphasis is on gnosis (metaphysical knowledge and solitude are the means of acquiring liberation and fulfillment), while in Yoga, the emphasis is on ascesis (liberation and fulfillment come through self-discipline and asceticism). Some historians of Indian philosophy (Surendranath Dasgupta and others) have conjectured that Samkhya was originally theistic but it became atheistic at a later stage under the influence of Carvaka and Pancasikha. But Max Muller believed that the Samkhya system is theistic because it admits in some form or other the existence of an Absolute and Supreme being. On the Yoga system there is no controversy—it has remained theistic throughout.