Pyrrho of Elis (c. 360-c. 270 BCE) usually is credited with founding this school of skeptical philosophy. He traveled to India with Alexander the Great's army and studied with the magi and the gymnosophists. Pyrrhonism as a school was either revitalized or re-founded by Aenesidemus in the first century BCE.
Pyrrhonism's objective is principally psychological, although it is best known for its epistemological arguments, particularly the problem of the criterion and the problem of induction. Through epoché (suspension of judgment) the mind is brought to ataraxia, a state of equanimity. As in Stoicism and Epicureanism, eudaimonia is the Pyrrhonist goal of life, and all three philosophies placed it in ataraxia or apatheia. According to the Pyrrhonists, it is one's opinions about non-evident matters that prevent one from attaining eudaimonia.
The main principle of Pyrrho's thought is expressed by the word acatalepsia, which connotes the ability to withhold assent from doctrines regarding the truth of things in their own nature; against every statement its contradiction may be advanced with equal justification.
Pyrrhonists withhold assent with regard to non-evident propositions, that is, dogma. They disputed that the dogmatists had found truth regarding non-evident matters. For any non-evident matter, a Pyrrhonist tries to make the arguments for and against such that the matter cannot be concluded, thus suspending belief. According to Pyrrhonism, even the statement that nothing can be known is dogmatic. They thus attempted to make their skepticism universal, and to escape the reproach of basing it upon a fresh dogmatism. Mental imperturbability (ataraxia) was the result to be attained by cultivating such a frame of mind.