Astika ("there is, there exists") and nastika ("not astika") are concepts used by the Brahmanical tradition, and modern scholars to classify and contrast Indian philosophies. Astika has been defined in one of three ways; as those who accept the epistemic authority of the Vedas, as those who accept the existence of atman, or as those who accept the existence of Ishvara. In contrast, nastika are those who deny the respective foundational definitions of astika.