Skepticism
From the 4th century BCE
The tradition of doubting claims to knowledge, from ancient philosophers seeking calm to modern arguments about dreams and demons.
The core idea
Ancient scepticism had two branches. Pyrrhonists, following Pyrrho of Elis and recorded by Sextus Empiricus, set every argument against an equally strong counter-argument and suspended judgement, finding that peace of mind followed. Academic sceptics, in Plato's own Academy, argued that nothing can be known for certain but that some things are more plausible than others.
Modern scepticism usually means a challenge rather than a way of life. René Descartes raised the possibility of an Descartes' evil demon in order to defeat it; David Hume concluded that our beliefs about causes and the future rest on habit rather than reason. Today the challenge is often posed as the brain in a vat.
Few philosophers call themselves sceptics, but nearly every theory of knowledge has to explain where the sceptic goes wrong. See the skepticism entry for the main responses.
What they hold
- For any claim, an argument of equal weight can be set against it.
- We cannot rule out scenarios in which our experience is systematically misleading.
- Any chain of justification ends in an assumption, an infinite regress or a circle.
- For the ancient sceptics, suspending judgement brings tranquillity.
The main criticisms
Critics charge that radical scepticism refutes itself: to claim that nothing can be known is to claim to know something. Others, such as G. E. Moore, reply that we are more certain that we have hands than we could ever be of the premises of a sceptical argument. Contextualists and externalists argue that the sceptic sets impossibly high standards for knowledge.
Key figures
Where it comes up
Further reading
- EncyclopediaStanford Encyclopedia of Philosophy: Ancient Skepticism
- WikipediaPhilosophical skepticism