---
title: "Philosophical skepticism"
chunk: 1/9
source: "https://en.wikipedia.org/wiki/Philosophical_skepticism"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T03:37:00.045187+00:00"
instance: "kb-cron"
---

Philosophical skepticism (UK spelling: scepticism; from Greek σκέψις skepsis, "inquiry") is a family of philosophical views that question the possibility of knowledge. It differs from other forms of skepticism in that it even rejects very plausible knowledge claims that belong to basic common sense. Philosophical skeptics are often classified into two general categories: Those who deny all possibility of knowledge, and those who advocate for the suspension of judgment due to the inadequacy of evidence. This distinction is modeled after the differences between the Academic skeptics and the Pyrrhonian skeptics in ancient Greek philosophy. Pyrrhonian skepticism is a practice of suspending judgment, and skepticism in this sense is understood as a way of life that helps the practitioner achieve inner peace. Some types of philosophical skepticism reject all forms of knowledge while others limit this rejection to certain fields, for example, knowledge about moral doctrines or about the external world. Some theorists criticize philosophical skepticism based on the claim that it is a self-refuting idea since its proponents seem to claim to know that there is no knowledge. Other objections focus on its implausibility and distance from regular life.

== Overview ==

Philosophical skepticism is a doubtful attitude toward commonly accepted knowledge claims. Skepticism in general is a questioning attitude toward all kinds of knowledge claims. In this wide sense, it is quite common in everyday life: many people are ordinary skeptics about parapsychology or about astrology because they doubt the claims made by proponents of these fields. But the same people are not skeptical about other knowledge claims like the ones found in regular school books. Philosophical skepticism differs from ordinary skepticism in that it even rejects knowledge claims that belong to basic common sense and seem to be very certain. For this reason, it is sometimes referred to as radical doubt. In some cases, it is even proclaimed that one does not know that "I have two hands" or that "the sun will come out tomorrow". In this regard, philosophical skepticism is not a position commonly adopted by regular people in everyday life. This denial of knowledge is usually associated with the demand that one should suspend one's beliefs about the doubted proposition. This means that one should neither believe nor disbelieve it but keep an open mind without committing oneself one way or the other. Philosophical skepticism is often based on the idea that no matter how certain one is about a given belief, one could still be wrong about it. From this observation, it is argued that the belief does not amount to knowledge. Philosophical skepticism follows from the consideration that this might be the case for most or all beliefs. Because of its wide-ranging consequences, it is of central interest to theories of knowledge since it questions their very foundations.
According to some definitions, philosophical skepticism is not just the rejection of some forms of commonly accepted knowledge but the rejection of all forms of knowledge. In this regard, we may have relatively secure beliefs in some cases but these beliefs never amount to knowledge. Weaker forms of philosophical skepticism restrict this rejection to specific fields, like the external world or moral doctrines. In some cases, knowledge per se is not rejected but it is still denied that one can ever be absolutely certain.
There are only few defenders of philosophical skepticism in the strong sense. In this regard, it is much more commonly used as a theoretical tool to test theories. On this view, it is a philosophical methodology that can be utilized to probe a theory to find its weak points, either to expose it or to modify it in order to arrive at a better version of it. However, some theorists distinguish philosophical skepticism from methodological skepticism in that philosophical skepticism is an approach that questions the possibility of certainty in knowledge, whereas methodological skepticism is an approach that subjects all knowledge claims to scrutiny with the goal of sorting out true from false claims. Similarly, scientific skepticism differs from philosophical skepticism in that scientific skepticism is an epistemological position in which one questions the veracity of claims lacking empirical evidence. In practice, the term most commonly references the examination of claims and theories that appear to be pseudoscience, rather than the routine discussions and challenges among scientists.
In ancient philosophy, skepticism was seen not just as a theory about the existence of knowledge but as a way of life. This outlook is motivated by the idea that suspending one's judgment on all kinds of issues brings with it inner peace and thereby contributes to the skeptic's happiness.

=== Classification ===
Skepticism can be classified according to its scope. Local skepticism involves being skeptical about particular areas of knowledge (e.g. moral skepticism, skepticism about the external world, or skepticism about other minds), whereas radical skepticism claims that one cannot know anything—including that one cannot know about knowing anything.
Skepticism can also be classified according to its method. Western philosophy has two basic approaches to skepticism. Cartesian skepticism—named somewhat misleadingly after René Descartes, who was not a skeptic but used some traditional skeptical arguments in his Meditations to help establish his rationalist approach to knowledge—attempts to show that any proposed knowledge claim can be doubted. Agrippan skepticism focuses on justification rather than the possibility of doubt. According to this view, none of the ways in which one might attempt to justify a claim are adequate. One can justify a claim based on other claims, but this leads to an infinite regress of justifications. One can use a dogmatic assertion, but this is not a justification. One can use circular reasoning, but this fails to justify the conclusion.