citing the Buddhist Samaññaphala Sutta, suggests six schools of heterodox, pre-Buddhist and pre-Jain, atheistic Indian traditions in 6th century BCE, that included Charvakas and Ajivikas. Charvaka was a living philosophy up to the 12th century in India's historical timeline, after which this system seems to have disappeared without leaving any trace. Philosophy The Charvaka school of philosophy had a variety of atheistic and materialistic beliefs. They held perception and direct experiments to be the valid and reliable source of knowledge. Epistemology The Charvaka epistemology holds perception as the primary and proper source of knowledge, while inference is held as prone to being either right or wrong and therefore conditional or invalid. Perceptions are of two types, for Charvaka, external and internal. External perception is described as that arising from the interaction of five senses and worldly objects, while internal perception is described by this school as that of inner sense, the mind. Inference is described as deriving a new conclusion and truth from one or more observations and previous truths. To Charvakas, inference is useful but prone to error, as inferred truths can never be without doubt. Inference is good and helpful, it is the validity of inference that is suspect – sometimes in certain cases and often in others. To the Charvakas there were no reliable means by which the efficacy of inference as a means of knowledge could be established. Charvaka's epistemological argument can be explained with the example of fire and smoke. Kamal states that when there is smoke (middle term), one's tendency may be to leap to the conclusion that it must be caused by fire (major term in logic). While this is often true, it need not be universally true, everywhere or all the times, stated the Charvaka scholars. Smoke can have other causes. In Charvaka epistemology, as long as the relation between two phenomena, or observation and truth, has not been proven as unconditional, it is an uncertain truth. In this Indian philosophy such a method of reasoning, that is jumping to conclusions or inference, is prone to flaw. Charvakas further state that full knowledge is reached when we know all observations, all premises and all conditions. But the absence of conditions, state Charvakas, can not be established beyond doubt by perception, as some conditions may be hidden or escape our ability to observe. They acknowledge that every person relies on inference in daily