In 1920, G. E. Moore returned to the University of Cambridge as Professor of Philosophy. British philosophy was still strongly shaped by absolute idealism (the view that reality is fundamentally mental), which often fueled doubts about the external world. Moore’s later “common-sense” rebuttal to skepticism grew out of this setting.
During the early 1920s Moore increasingly argued that philosophy should start from what we ordinarily know—such as that we have bodies and live on Earth—rather than from abstract theories that overturn everyday knowledge. This approach aimed to undercut radical skepticism, which claims we cannot know basic facts about the world. Moore’s strategy was not to deny that skeptical arguments exist, but to challenge whether they can outweigh everyday certainty.
In 1925, Moore published “A Defence of Common Sense.” He listed “truisms” he said we know with certainty (for example, that the Earth existed before his birth and that his body existed yesterday). The essay argued that skeptical or idealist conclusions are less credible than these common-sense claims, so philosophy should not abandon them lightly.
After 1925, Moore’s list of truisms became a clear test case for debates about skepticism and knowledge. Critics pressed him on how we know such claims and whether “common sense” is evidence or merely habit. The discussion helped shift epistemology toward questions about justification, proof, and the limits of doubt.
Across the late 1920s and 1930s, Moore’s teaching and writing made him a central reference point for Cambridge philosophers debating realism, skepticism, and analysis of ordinary statements. His emphasis on careful distinction between a claim’s ordinary meaning and a philosopher’s theory about it shaped how later thinkers assessed skeptical arguments. This period set the stage for direct engagement with Wittgenstein and Malcolm.
In 1939, Moore delivered and published “Proof of an External World.” He argued that by showing his hands and asserting “Here is one hand” and “Here is another,” he could prove at least two external objects exist—so an external world exists. Moore also stated conditions for a proper proof: the premises must differ from the conclusion, be known, and entail the conclusion.
In April 1939, Moore read a paper titled “Certainty” to the Cambridge University Moral Sciences Club. The discussion highlighted a key theme in Moore’s anti-skeptical approach: some propositions (like “Here is a hand”) seem more secure than philosophical premises used to doubt them. This event also connected Moore’s work directly to later debates about what “certainty” amounts to.
After 1939, Moore’s “here is one hand” argument became a standard reference in discussions of radical skepticism. Supporters treated it as showing that skeptical standards of proof are misplaced in everyday knowledge, while critics argued it “begs the question” against the skeptic. Either way, it forced later philosophers to clarify what counts as evidence and what kinds of doubt are meaningful.
In 1942, Moore published “A Reply to My Critics” in The Philosophy of G. E. Moore, addressing objections to his method and conclusions. The exchange clarified how Moore understood ordinary propositions, knowledge claims, and philosophical analysis. This helped consolidate “common-sense” realism as a major position within analytic philosophy.
In 1950–1951, Ludwig Wittgenstein wrote remarks later published as On Certainty, explicitly responding to Moore’s claims about knowing common-sense propositions with certainty. Wittgenstein argued that meaningful doubt depends on a background of propositions that “stand fast” in practice (often called hinge propositions). This reframed Moore’s project: the issue became not just proving the external world, but understanding the role of certainty in language and inquiry.
In 1951, Moore delivered “Four Forms of Skepticism,” distinguishing different skeptical challenges instead of treating skepticism as a single problem. This late work shows Moore still refining how to answer doubts about the external world, other minds, and knowledge of the past. It also illustrates the lasting importance of his common-sense strategy well into mid-century analytic philosophy.
G. E. Moore died in October 1958, marking an endpoint for the period when he personally shaped the common-sense rebuttal to skepticism through lectures, papers, and replies to critics. By then, his key anti-skeptical works—especially “A Defence of Common Sense” (1925) and “Proof of an External World” (1939)—had become central reference points. The debates he sparked continued through later publications and responses, including Wittgenstein’s posthumous On Certainty.
G. E. Moore and the Common-Sense Rebuttal to Skepticism (1920–1959)