Epicurus and his followers had a well-developed epistemology, which developed as a result of their rivalry with other philosophical schools. Epicurus wrote a treatise entitled , or Rule, in which he explained his methods of investigation and theory of knowledge. This book, however, has not survived, nor does any other text that fully and clearly explains Epicurean epistemology, leaving only mentions of this epistemology by several authors to reconstruct it. Epicurus was an ardent Empiricist; believing that the senses are the only reliable sources of information about the world. He rejected the Platonic idea of "Reason" as a reliable source of knowledge about the world apart from the senses and was bitterly opposed to the Pyrrhonists and Academic Skeptics, who not only questioned the ability of the senses to provide accurate knowledge about the world, but also whether it is even possible to know anything about the world at all.
