||Indian Philosophy encompasses the systems of thought and reflection that developed on the Indian subcontinent. They include philosophical systems generally classified as orthodox (astika, from the Sanskrit asti "there is") such as Nyāya ("Rule" or "Method"), Vaiśeṣika ("Particular"), Saṃkhya ("Enumeration" or "Number"), Yoga ("Union"), Mīmāṃsā ("Reflection" or "Critical Investigation") and Vedanta ("conclusion of the Veda"). They are classified as orthodox because they rely on the authority of the Vedas (an ancient collection of hymns of religio-philosophical nature). In contrast, the heterodox (nāstika) systems of thought reject the authority of the Vedas and the superiority of Brahmins in matters of philosophical reflection. Besides Buddhism, the other heterodox schools include the Jainas ("Followers of Conquerors", from the Sanskrit verb ji "to conquer"), the ascetic Ājīvikas, and the Cārvākas materialists. Given the diversity of views, theories, and doctrines espoused by philosophers on the Indian subcontinent, there is no unifying thread or single characteristic that would be common to all. Although all the orthodox systems profess some allegiance to the Vedas, they range widely in their interpretations of Vedic statements and pursue their speculative ventures unhindered by tradition (the acceptance of the Vedas is often just a convenient device for a philosopher to gain acceptance in orthodox circles). Among the key concepts of Indian Philosophy are those of karma ("action," which addresses the moral efficiency of human actions), atman ("self," which stands for the sense of an absolute or transcendental spirit or self) and its countervailing notion of anatman ("not-self") in Buddhism, mokṣa ("liberation," conceived as the highest ideal of moral and spiritual cultivation), and the similarly formed ideal of nirvāṇa ("cessation") in Buddhism. A great deal of philosophical speculation in India is concerned with establishing reliable sources of knowing (pramāṇas) such that metaphysical concerns about the nature of reality are seldom pursued in isolation from logical and epistemological concerns about the nature of knowledge and its sources. Indian philosophy is comparable in the range and scope of its metaphysical, epistemological, and ethical concerns with Western philosophy, although philosophers in India have also pursued problems that their Western counterparts never did. Examples include such matters as the source (utpatti) and apprehension (jñapti) of reliable cognitions (prāmāṇya). Likewise, there are problems central to Western philosophy (e.g., whether knowledge arises from experience or from reason) that philosophers in India did not pursue, and important distinctions (such as that between analytic and synthetic judgments) they did not make.