---
title: "Philosophical skepticism"
chunk: 2/9
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"
---

=== Skeptical scenarios ===
A skeptical scenario is a hypothetical situation which can be used in an argument for skepticism about a particular claim or class of claims. Usually the scenario posits the existence of a deceptive power that deceives our senses and undermines the justification of knowledge otherwise accepted as justified, and is proposed in order to call into question our ordinary claims to knowledge on the grounds that we cannot exclude the possibility of skeptical scenarios being true. Skeptical scenarios have received a great deal of attention in modern Western philosophy.
The first major skeptical scenario in modern Western philosophy appears in René Descartes's Meditations on First Philosophy. At the end of the first Meditation Descartes writes:  "I will suppose ... that some evil demon of the utmost power and cunning has employed all his energies to deceive me."

The "evil demon problem", also known as "Descartes's evil demon", was first proposed by René Descartes. It invokes the possibility of a being who could deliberately mislead one into falsely believing everything that you take to be true.
The "brain in a vat" hypothesis is cast in contemporary scientific terms. It supposes that one might be a disembodied brain kept alive in a vat and fed false sensory signals by a mad scientist. Further, it asserts that since a brain in a vat would have no way of knowing that it was a brain in a vat, you cannot prove that you are not a brain in a vat.
The "dream argument", proposed by both René Descartes and Zhuangzi, supposes reality to be indistinguishable from a dream.
The "five minute hypothesis", most notably proposed by Bertrand Russell, suggests that we cannot prove that the world was not created five minutes ago (along with false memories and false evidence suggesting that it was not only five minutes old).
The "simulated reality hypothesis" or "Matrix hypothesis" suggests that everyone, or even the entire universe, might be inside a computer simulation or virtual reality.
The "Solipsistic" theory that claims that knowledge of the world is an illusion of the Self.

=== Epistemological skepticism ===
Skepticism, as an epistemological view, calls into question whether knowledge is possible at all. This is distinct from other known skeptical practices, including Cartesian skepticism, as it targets knowledge in general instead of individual types of knowledge.
Skeptics argue that belief in something does not justify an assertion of knowledge of it. In this, skeptics oppose foundationalism, which states that there are basic positions that are self-justified or beyond justification, without reference to others. (One example of such foundationalism may be found in Spinoza's Ethics.)
Among other arguments, skeptics use the Münchhausen trilemma and the problem of the criterion to claim that no certain belief can be achieved. This position is known as "global skepticism" or "radical skepticism." Foundationalists have used the same trilemma as a justification for demanding the validity of basic beliefs. Epistemological nihilism rejects the possibility of human knowledge, but not necessarily knowledge in general.
There are two different categories of epistemological skepticism, which can be referred to as mitigated and unmitigated skepticism. The two forms are contrasting but are still true forms of skepticism. Mitigated skepticism does not accept "strong" or "strict" knowledge claims but does, however, approve specific weaker ones. These weaker claims can be assigned the title of "virtual knowledge", but must be to justified belief. Some mitigated skeptics are also fallibilists, arguing that knowledge does not require certainty. Mitigated skeptics hold that knowledge does not require certainty and that many beliefs are, in practice, certain to the point that they can be safely acted upon in order to live significant and meaningful lives. Unmitigated skepticism rejects both claims of virtual knowledge and strong knowledge. Characterizing knowledge as strong, weak, virtual or genuine can be determined differently depending on a person's viewpoint as well as their characterization of knowledge. Unmitigated skeptics believe that objective truths are unknowable and that man should live in an isolated environment in order to win mental peace. This is because everything, according to them, is changing and relative. The refusal to make judgments is of uttermost importance since there is no knowledge; only probable opinions.