One ancient Greek sceptic refused to speak and just wiggled his finger
Cratylus decided that meanings shift so constantly that communication is impossible, so he stopped talking and wagged a finger instead. Few sceptics went that far, but the tradition he belonged to, doubting what others take for granted, helped give birth to the scientific method and still resists every attempt at refutation.
Scepticism is doubt towards claims that look like mere belief or dogma. A sceptic about a claim usually recommends neither believing nor disbelieving it, but suspending judgement, especially when the evidence is thin or experts disagree. The word comes from the Greek skeptomai, to search or look into. Some thinkers separate a healthy scepticism that demands strong evidence from a radical kind that suspends judgement forever, even against demonstrable truth.
Philosophical scepticism is the rare, radical variety. Where ordinary people doubt astrologers, philosophical sceptics question things that seem obvious, such as whether you know you have two hands or that the sun will rise tomorrow. It is taken seriously because nobody has managed to refute it conclusively. The historian Richard Popkin even described the history of philosophy as partly a struggle with scepticism, a struggle that led many modern philosophers to give up hunting for perfectly certain first principles.
It arose independently in Greece and India. In India the Ajñana school was an early rival of Buddhism and Jainism; two of the Buddha's leading disciples, Sariputta and Moggallāna, first studied under the Ajñana teacher Sanjaya Belatthiputta. In Greece, Xenophanes voiced doubts in the sixth century BCE, and the Sophist Gorgias reputedly argued that nothing exists, that if it did we could not know it, and that if we knew it we could not tell anyone. Socrates claimed to know nothing worthwhile.
Two formal schools followed. Pyrrho of Elis founded Pyrrhonism, which urged suspending judgement to reach tranquillity of mind, holding that equally strong arguments exist on both sides of any dispute. Academic scepticism, led by Arcesilaus and Carneades at Plato's own Academy, denied that knowledge is possible but allowed some beliefs to be more probable than others. Almost all their writings are lost; most of what survives comes through Sextus Empiricus. In science and medicine, the same doubting habit drove the insistence on testing claims by experiment rather than tradition.
Source: Skepticism
