---
title: "Philosophical skepticism"
chunk: 7/9
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"
---

==== David Hume (1711–1776) ====
David Hume was among the most influential proponents of philosophical skepticism during the Age of Enlightenment and one of the most notable voices of the Scottish Enlightenment and British Empiricism. He especially espoused skepticism regarding inductive reasoning, and questioned what the foundation of morality was, creating the is–ought problem. His approach to skepticism is considered even more radical than that of Descartes.
Hume argued that any coherent idea must be either a mental copy of an impression (a direct sensory perception) or copies of multiple impressions innovatively combined. Since certain human activities like religion, superstition, and metaphysics are not premised on any actual sense-impressions, their claims to knowledge are logically unjustified. Furthermore, Hume even demonstrates that science is merely a psychological phenomenon based on the association of ideas: often, specifically, an assumption of cause-and-effect relationships that is itself not grounded in any sense-impressions. Thus, even scientific knowledge is logically unjustified, being not actually objective or provable but, rather, mere conjecture flimsily based on our minds perceiving regular correlations between distinct events. Hume thus falls into extreme skepticism regarding the possibility of any certain knowledge. Ultimately, he offers that, at best, a science of human nature is the "only solid foundation for the other sciences".

==== Immanuel Kant (1724–1804) ====

Immanuel Kant (1724–1804) tried to provide a ground for empirical science against David Hume's skeptical treatment of the notion of cause and effect.  Hume (1711–1776) argued that for the notion of cause and effect no analysis is possible which is also acceptable to the empiricist program primarily outlined by John Locke (1632–1704).  But, Kant's attempt to give a ground to knowledge in the empirical sciences at the same time cut off the possibility of knowledge of any other knowledge, especially what Kant called "metaphysical knowledge". So, for Kant, empirical science was legitimate, but metaphysics and philosophy was mostly illegitimate. The most important exception to this demarcation of the legitimate from the illegitimate was ethics, the principles of which Kant argued can be known by pure reason without appeal to the principles required for empirical knowledge.  Thus, with respect to metaphysics and philosophy in general (ethics being the exception), Kant was a skeptic. This skepticism as well as the explicit skepticism of G. E. Schulze gave rise to a robust discussion of skepticism in German idealistic philosophy, especially by Hegel.  Kant's idea was that the real world (the noumenon or thing-in-itself) was inaccessible to human reason (though the empirical world of nature can be known to human understanding) and therefore we can never know anything about the ultimate reality of the world.  Hegel argued against Kant that although Kant was right that using what Hegel called "finite" concepts of "the understanding" precluded knowledge of reality, we were not constrained to use only "finite" concepts and could actually acquire knowledge of reality using "infinite concepts" that arise from self-consciousness.

=== Skepticism in the 20th century and contemporary philosophy ===
G. E. Moore famously presented the "Here is one hand" argument against skepticism in his 1925 paper, "A Defence of Common Sense". Moore claimed that he could prove that the external world exists by simply presenting the following argument while holding up his hands: "Here is one hand; here is another hand; therefore, there are at least two objects; therefore, external-world skepticism fails". His argument was developed for the purpose of vindicating common sense and refuting skepticism. Ludwig Wittgenstein later argued in his On Certainty (posthumously published in 1969) that Moore's argument rested on the way that ordinary language is used, rather than on anything about knowledge.
In contemporary philosophy, Richard Popkin was a particularly influential scholar on the topic of skepticism. His account of the history of skepticism given in The History of Scepticism from Savonarola to Bayle (first edition published as The History of Scepticism From Erasmus to Descartes) was accepted as the standard for contemporary scholarship in the area for decades after its release in 1960. Barry Stroud also published a number of works on philosophical skepticism, most notably his 1984 monograph, The Significance of Philosophical Scepticism. From the mid-1990s, Stroud, alongside Richard Fumerton, put forward influential anti-externalist arguments in favor of a position called "metaepistemological scepticism". Other contemporary philosophers known for their work on skepticism include James Pryor, Keith DeRose, and Peter Klein.

== History of skepticism in non-Western philosophy ==

=== Ancient Indian skepticism ===

==== Ajñana ====

Ajñana (literally 'non-knowledge') were the skeptical school of ancient Indian philosophy. It was a śramaṇa movement and a major rival of early Buddhism and Jainism. They have been recorded in Buddhist and Jain texts. They held that it was impossible to obtain knowledge of metaphysical nature or ascertain the truth value of philosophical propositions; and even if knowledge was possible, it was useless and disadvantageous for final salvation.

==== Buddhism ====