Can we be certain of anything?

Certainty: A belief held so securely that error appears impossible, not merely unlikely.

Scepticism: The challenge that our usual grounds for knowledge may not rule out error.

Justification: The reasons or evidence that make a belief responsibly held.

Infallibilism: The view that knowledge requires grounds that cannot coexist with error.

External world: A reality existing independently of a person's present experience of it.

René Descartes: Descartes deliberately withholds assent from anything open to doubt. Dreams and a powerful deceiver unsettle sense experience and reasoning, while the act of thinking appears to survive the test. His method asks whether knowledge can be rebuilt only after a perfectly secure foundation has been found. David Hume: Hume treats many of our expectations as habits formed by experience, not conclusions reason alone can secure. The world has behaved itself so far; that is not a proof that it will continue to do so. His challenge is less a dramatic deception than the gap between repeated experience and certainty about what must happen next. G. E. Moore: Moore resists scepticism by beginning with ordinary knowledge: he knows that he has hands and that an external world exists. The dispute is over which claim deserves greater confidence: the familiar judgement or the philosophical premise that seems to undermine it.

David Hume: Hume treats many of our expectations as habits formed by experience, not conclusions reason alone can secure. The world has behaved itself so far; that is not a proof that it will continue to do so. His challenge is less a dramatic deception than the gap between repeated experience and certainty about what must happen next. G. E. Moore: Moore resists scepticism by beginning with ordinary knowledge: he knows that he has hands and that an external world exists. The dispute is over which claim deserves greater confidence: the familiar judgement or the philosophical premise that seems to undermine it. Ludwig Wittgenstein: Wittgenstein examines the background certainties that make inquiry possible. Some commitments are not conclusions reached from evidence; they are the fixed points around which checking, doubting and giving reasons operate. Universal doubt may therefore remove the very practices that give the word doubt its sense.

G. E. Moore: Moore resists scepticism by beginning with ordinary knowledge: he knows that he has hands and that an external world exists. The dispute is over which claim deserves greater confidence: the familiar judgement or the philosophical premise that seems to undermine it. Ludwig Wittgenstein: Wittgenstein examines the background certainties that make inquiry possible. Some commitments are not conclusions reached from evidence; they are the fixed points around which checking, doubting and giving reasons operate. Universal doubt may therefore remove the very practices that give the word doubt its sense. René Descartes: Descartes deliberately withholds assent from anything open to doubt. Dreams and a powerful deceiver unsettle sense experience and reasoning, while the act of thinking appears to survive the test. His method asks whether knowledge can be rebuilt only after a perfectly secure foundation has been found.

A conclusion needs support from the stated reasons. Here, an extra linking premise is required before the consequence follows.

Whether a thinker is likeable does not establish whether their argument is sound. The reasons themselves must be assessed.

The portrait belongs to the named philosopher. Follow the profile link in the feedback to revisit their central move.

The portrait belongs to the named philosopher. Follow the profile link in the feedback to revisit their central move.

The first pair develops “Knowledge must rule out every possibility of error.”; the second pair applies pressure from the rival position “Reliable, well-justified belief is enough for knowledge.”.

The first pair develops “Reliable, well-justified belief is enough for knowledge.”; the second pair applies pressure from the rival position “Common-sense certainty is more secure than abstract doubt.”.

The first pair develops “Common-sense certainty is more secure than abstract doubt.”; the second pair applies pressure from the rival position “Knowledge must rule out every possibility of error.”.