The Nyāya school of Hinduism developed and refined many treatises on epistemology that widely influenced other schools of Hinduism. Nyāya treated it as theory of knowledge, and its scholars developed it as Pramana-sastras. Pramana, a Sanskrit word, literally is "means of knowledge". It encompasses one or more reliable and valid means by which human beings gain accurate, true knowledge. The focus of Pramana is how correct knowledge can be acquired, how one knows, how one doesn't, and to what extent knowledge pertinent about someone or something can be acquired.
The Naiyayikas (the Nyāya scholars) accepted four valid means (pramaṇa) of obtaining valid knowledge (pramana) – perception (pratyakṣa), inference (anumāna), comparison (upamāna) and word/testimony of reliable sources (śabda). The Nyāya scholars, along with those from other schools of Hinduism, also developed a theory of error, to methodically establish means to identify errors and the process by which errors are made in human pursuit of knowledge. These include Saṁśaya (समस्या, problems, inconsistencies, doubts) and Viparyaya (विपर्यय, contrariness, errors) which can be corrected or resolved by a systematic process of Tarka (तर्क, reasoning, technique).