Responses to External World Skepticism

Core Idea

Responses to external world skepticism target different premises in the skeptical argument. G.E. Moore's commonsense response ('Here is a hand') uses closure to reverse the skeptical argument: if I know I have hands, and knowing I have hands entails knowing I'm not a BIV, then I know I'm not a BIV. Contextualists argue that 'know' expresses different standards in different contexts, so skeptics raise the bar artificially high. Dogmatists like Pryor claim that perceptual experience provides immediate, defeasible justification for beliefs about the external world without needing to antecedently refute skeptical hypotheses. Abductive responses argue that the hypothesis of a coherent external world is the best explanation of the coherence of our experiences.

How It's Best Learned

Map each response onto the specific premise of the skeptical argument it denies. This reveals that Moore denies modus ponens in the skeptic's direction, contextualists deny that standards are fixed, and dogmatists deny that we need independent grounds before perceptual justification takes hold.

Common Misconceptions

• Moore's 'here is a hand' argument is not naive; it is a sophisticated claim that certainty about ordinary things can be more secure than philosophical premises.
• Contextualism does not say skeptics are wrong; it says their knowledge attributions are true in their high-standards context but irrelevant to ordinary epistemic practice.

Explainer

You've already studied the skeptical argument in detail. Recall its structure: (1) You can't rule out that you're a Brain in a Vat (BIV). (2) If you can't rule out being a BIV, you don't know you have hands. (3) Therefore, you don't know you have hands. The argument is valid — if the premises are true, the conclusion follows. What makes it hard to dismiss is that premise (1) seems obviously correct: you have no direct evidence against the BIV scenario. Responses to skepticism each target a different premise or a hidden assumption, and understanding each response requires seeing exactly what it denies.

G.E. Moore's commonsense response is more philosophically sophisticated than it initially appears. Moore doesn't argue against the skeptical premises — instead he reverses the argument's direction. He says: I know I have hands (that's more certain than any philosophical premise). Knowing I have hands entails knowing I'm not a BIV. Therefore, I know I'm not a BIV. This is called Moorean shift — using a highly certain ordinary belief to discharge the skeptical hypothesis rather than refuting the hypothesis directly. The key insight is about relative certainty: we are far more justified in believing "I have hands" than we are in believing any philosophical premise that would lead us to doubt it. Moore is exploiting epistemic closure — the principle that knowledge transfers across known entailments — but running it in the direction opposite to the skeptic.

Contextualism denies that "know" means the same thing in every context. In a philosophy seminar, the word "know" invokes very high standards — only beliefs that are impervious to all conceivable alternatives count. In ordinary life, the word "know" invokes much lower standards — you need only rule out relevant, realistic alternatives. When the skeptic says you don't know you have hands, they're operating at philosophical seminar standards. That's true — at those standards, you don't know. But those standards are irrelevant to whether you know you have hands in the supermarket. Contextualism preserves both the intuition that the skeptic says something true and the intuition that you genuinely know ordinary things; it just says they're talking about knowledge at different contextual levels.

Dogmatism (associated with Jim Pryor) attacks the skeptical argument's presupposition that you need to *antecedently* refute skeptical hypotheses before your perceptual beliefs are justified. Dogmatists deny this: when you have a perceptual experience of a hand, that experience itself immediately confers *prima facie* justification on the belief "I have a hand," without needing to first rule out BIV scenarios. The skeptic can't demand that you discharge the BIV hypothesis before perception counts as justification — that reverses the epistemic order. Perception is your *starting point*, not a conclusion to be earned. Finally, the abductive response treats the question as a competition between hypotheses: the hypothesis that a coherent external world exists is simply a better explanation of why your experiences cohere as well as they do than the hypothesis that a malicious demon is systematically deceiving you. Inference to the best explanation, your prerequisite concept from rationalism vs. empiricism, gives you positive reason to believe in the external world.