Charvaka (; IAST: Cārvāka), also known as Lokāyata, is an ancient school of Indian materialism. Charvaka holds direct perception, empiricism, and conditional inference as proper sources of knowledge, embraces philosophical skepticism and rejects ritualism and supernaturalism. It was a popular belief system in ancient India. Brihaspati, a philosopher, is traditionally referred to as the founder of Charvaka or Lokāyata philosophy, although some scholars dispute this. During the Hindu reformation period in the first millennium BCE, when Buddhism was established by Gautama Buddha and Jainism was re-organized by Parshvanatha, the Charvaka philosophy was well documented and opposed by both religions. Much of the primary literature of Charvaka, the Barhaspatya sutras, were lost either due to waning popularity or other unknown reasons. Its teachings have been compiled from historic secondary literature such as those found in the shastras, sutras, and the Indian epic poetry as well as in the dialogues of Gautama Buddha and from Jain literature. However, there is text that may belong to the Charvaka tradition, written by the skeptic philosopher Jayarāśi Bhaṭṭa, known as the Tattvôpaplava-siṁha, that provides information about this school, albeit unorthodox. One of the widely studied principles of Charvaka philosophy was its rejection of inference as a means to establish valid, universal knowledge, and metaphysical truths. In other words, the Charvaka epistemology states that whenever one infers a truth from a set of observations or truths, one must acknowledge doubt; inferred knowledge is conditional. Charvaka is categorized as one of the nāstika or "heterodox" schools of Indian philosophy. It is considered an example of atheistic schools in the Hindu tradition. Etymology and meaning The etymology of Charvaka (Sanskrit: चार्वाक) is uncertain. Bhattacharya quotes the grammarian Hemacandra, to the effect that the word cārvāka is derived from the root , 'to chew' : "A Cārvāka chews the self (carvatyātmānaṃ cārvākaḥ). Hemacandra refers to his own grammatical work, Uṇādisūtra 37, which runs as follows: mavāka-śyāmāka-vārtāka-jyontāka-gūvāka-bhadrākādayaḥ. Each of these words ends with the āka suffix and is formed irregularly." This may also allude to the philosophy's hedonistic precepts of "eat, drink, and be merry". Others believe it to mean "agreeable speech" or pejoratively, "sweet-tongued", from Sanskrit's "agreeable" and "speech" (which becomes in the nominative singular and in compounds). Yet another hypothesis is that it is eponymous, with the founder of the school being Charvaka, a disciple of Brihaspati. As Lokayata According to claims of Debiprasad Chattopadhyaya, the traditional name