Essay: Proof of an External World

Overview
George Edward Moore's 1939 essay "Proof of an External World" delivers a compact, plainspoken challenge to philosophical skepticism by appealing to ordinary, commonsense claims. Moore insists that some simple propositions about the existence of external objects are more certain than the skeptical premises that deny them. The essay is notable for its iconoclastic tone and for treating everyday assertions as legitimate evidence against radical doubt.
Moore rejects elaborate epistemic theory as a prerequisite for accepting basic facts. Rather than engaging in subtle epistemological analysis, he offers an immediate demonstration designed to show that empirical knowledge of the external world is possible and that skepticism fails to overturn those facts.

Moore's Argument
The core of Moore's argument is famously humble and direct: he raises one hand and says, "Here is one hand," then raises the other and says, "Here is another hand," and concludes that an external world exists. He treats these demonstrations as straightforward pieces of evidence that prove the existence of external objects. Moore emphasizes that these assertions are known with greater certainty than the philosophical premises used to deny them, so the burden of proof lies with the skeptic.
Moore frames his move as a logical reply to skeptical reasoning. If a skeptic offers a general argument that appears to show that no knowledge of external things is possible, Moore suggests that the skeptic cannot legitimately claim victory if the demonstrative facts are more certain than the skeptic's general premises. The essay thereby flips the methodological question: certainty of ordinary propositions should take precedence unless the skeptic can show a specific, defeasible reason to doubt them.

Philosophical Significance
Moore's strategy embodies a shift away from seeking an infallible foundation for knowledge and toward treating common-sense beliefs as prima facie justified. He advances the idea that knowledge is not always hostage to theoretical refutation; one can know ordinary facts even if one cannot conclusively disprove every skeptical hypothesis. This pragmatic posture influenced later analytic and ordinary language philosophers who emphasized how philosophical problems can evaporate once surface grammar and common life are respected.
The essay also crystallizes a methodological tension in epistemology: whether philosophical scrutiny should start by doubting common beliefs or by accepting the certainty of some everyday propositions. Moore's insistence on granting priority to ordinary knowledge has been a touchstone for debates about the proper standards for knowledge claims and the standards skeptics must meet.

Reception and Criticism
"Proof of an External World" provoked widespread discussion and mixed reactions. Admirers praise Moore's clarity and his refusal to be paralyzed by skeptical scenarios, seeing his demonstration as a healthy corrective to unnecessary philosophical skepticism. His approach is credited with reinforcing the idea that philosophy should not undermine the obvious without very strong reasons.
Critics argue that Moore's move is question-begging: simply asserting "Here is a hand" does not engage the skeptic's challenge that appearances might be systematically misleading. Others contend that Moore conflates demonstration with refutation; a demonstration that an ordinary proposition is known does not, by itself, dismantle the skeptic's demand for epistemic justification. Nevertheless, the essay remains influential for its provocative simplicity and its enduring role in discussions of skepticism, knowledge, and common sense.