Scepticism (cont)

In philosophical skepticism, pyrrhonism is a position that refrains from making truth claims. A philosophical skeptic does not claim that truth is impossible (which itself would be a truth claim), instead it recommends "suspending belief". The term is commonly used to describe philosophies which are similar to philosophical skepticism, such as academic skepticism, an ancient variant of Platonism that claimed knowledge of truth was impossible. Empiricism is a closely related, but not identical, philosophy to philosophical skepticism. Empiricists claim empiricism is a pragmatic compromise between philosophical skepticism and nomothetic science; philosophical skepticism is in turn sometimes referred to as "radical empiricism."

Western Philosophical skepticism originated in ancient Greek philosophy. The Greek Sophists of the 5th century BC were partially skeptics.

Pyrrho of Elis (365–275 BC) is usually credited with founding the "school" of skepticism. He traveled to India and studied with the "gymnosophists" (naked lovers of wisdom), which could have been any number of Indian sects. From there, he brought back the idea that nothing can be known for certain. The senses are easily fooled, and reason follows too easily our desires. Pyrrhonism was a school of skepticism founded by his follower Aenesidemus in the first century BC and recorded by Sextus Empiricus in the late 2nd century or early 3rd century AD. Subsequently, in the "New Academy" Arcesilaus (c. 315–241 BC) and Carneades (c. 213–129 BC) developed more theoretical perspectives by which conceptions of absolute truth and falsity were refuted as uncertain. Carneades criticized the claims of the Dogmatists, especially supporters of Stoicism, asserting that absolute certainty of knowledge is impossible. Sextus Empiricus (c. AD 200), the main authority for Greek skepticism, developed the philosophy further, incorporating aspects of empiricism into the basis for asserting knowledge.

Greek skeptics criticized the Stoics, accusing them of dogmatism. For the skeptics, the logical mode of argument was untenable, as it relied on propositions which could not be said to be either true or false without relying on further propositions. This was the regress argument, whereby every proposition must rely on other propositions in order to maintain its validity (see the five tropes of Agrippa the Sceptic). In addition, the skeptics argued that two propositions could not rely on each other, as this would create a circular argument (as p implies q and q implies p). For the skeptics, such logic was thus an inadequate measure of truth and could create as many problems as it claimed to have solved. Truth was not, however, necessarily unobtainable, but rather an idea which did not yet exist in a pure form. Although skepticism was accused of denying the possibility of truth, in fact it appears to have mainly been a critical school which merely claimed that logicians had not discovered truth.

In Islamic philosophy, skepticism was established by Al-Ghazali (1058–1111), known in the West as "Algazel", as part of the Ash'arischool of Islamic theology, whose method of skepticism shares many similarities with Descartes' method.

In an effort to avoid skepticism, René Descartes begins his Meditations on First Philosophy attempting to find indubitable truth on which to base his knowledge. He later recognizes this truth as "I think, therefore I am," but before he finds this truth, he briefly entertains the skeptical arguments from dreaming and radical deception.

David Hume has also been described as a skeptic.

Pierre Le Morvan has distinguished between three philosophical approaches to skepticism. The first he terms the "Foil Approach." According to this approach, skepticism is treated as a problem to be solved, or challenge to be met, or threat to be parried; skepticism's value according to this method, insofar as it is deemed to have one, accrues from its role as a foil contrastively illuminating what is required for knowledge and justified belief. The second he calls the "Bypass Approach" according to which skepticism is bypassed as a major concern of epistemology. Le Morvan advocates a third approach—he dubs it the "Health Approach"—that explores when skepticism is healthy and when it is not, or when it is virtuous and when it is vicious.