Atheism (Sanskrit: nir-īśvara-vāda, lit. “statement of no Lord“, “doctrine of godlessness”) or disbelief in God or gods has been a historically propounded viewpoint in many of the orthodox and heterodox streams of Hindu philosophies. Generally, atheism is valid in Hinduism, but the path of the atheist is viewed as very difficult to follow in matters of spirituality.
The Sanskrit term Āstika (“pious, orthodox”) refers to the systems of thought which admit the validity of the Vedas. Sanskrit asti means “there is”, and Āstika (per Pāṇini 4.2.60) derives from the verb, meaning “one who says ‘asti’“.
Technically, in Hindu philosophy; the term Āstika refers only to acceptance of authority of Vedas, not belief in the existence of God. However, though not accepted universally; Āstika is sometimes translated as “theist” and Nāstika as “atheist“, assuming the rejection of Vedas to be synonymous to the rejection of God.
Among the six Astika schools of Hindu philosophy, the Samkhya do not accept God, and the early Mimamsa also rejected the notion of God. The early Mimamsa not only did not accept God but said that human action itself was enough to create the necessary circumstances for the enjoyment of its fruits.
The atheistic viewpoint as present in the Samkhya and Mimamsa schools of Hindu philosophy takes the form of rejecting a creator-God. The Samkhya school believed in a dual existence of Prakriti (“nature”) and Purusha (“spirit”) and had no place for an Ishvara (“God”) in its system. The early Mimamsakas believed in an adrishta (“unseen”) that resulted from performing karmas (“works”) and saw no need for an Ishvara in their system. Mimamsa, as a philosophy, deals exclusively with karma and thus is sometimes called Karma-Mimamsa. The karmas dealt with in Mimamsa concern the performance of Yajnas (“sacrifices to gods“) enjoined in the Vedas.