Pyrrhonism, or Pyrrhonian skepticism, was a school of skepticism founded by Aenesidemus in the 1st century BC and recorded by Sextus Empiricus in the late 2nd century or early 3rd century AD. It was named after Pyrrho, a philosopher who lived from c. 360 to c. 270 BC, although the relationship between the philosophy of the school and of the historical figure is murky. A renaissance of the term is to be noted for the 17th century when the modern scientific worldview was born.
Whereas academic skepticism, with Carneades as its most famous adherent, claims that "Nothing can be known, not even this", Pyrrhonian skeptics withhold any assent with regard to non-evident propositions and remain in a state of perpetual inquiry. They disputed the possibility of attaining truth by sensory apprehension, reason, or the two combined, and thence inferred the need for total suspension of judgment (epoché) on things. According to them, 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. As in Stoicism and Epicureanism, the happiness or satisfaction of the individual was the goal of life, and all three philosophies placed it in tranquility or indifference. According to the Pyrrhonists, it is our opinions or unwarranted judgments about things which turn them into desires, painful effort, and disappointment. From all this a person is delivered who abstains from judging one state to be preferable to another. But, as complete inactivity would have been synonymous with death, the skeptic, while retaining his consciousness of the complete uncertainty enveloping every step, might follow custom (or nature) in the ordinary affairs of life.