How did skepticism first develop in ancient Greece?

Skeptical attitudes in ancient Greece emerged around the 5th century BCE, rooted in the diverse inquiries of early thinkers. Philosophers such as the Eleatics challenged ordinary perceptions of reality, while Heracleitus and Xenophanes questioned the possibility of finding permanent, objective truth.1

This skepticism was further developed by Socrates, who famously questioned knowledge claims, and Sophists like Protagoras and Gorgias, who introduced themes of relativism and nihilism.1

The formalization of skepticism is attributed to Pyrrhon of Elis, who sought mental peace (ataraxia) by practicing epochē—the suspension of judgment regarding the nature of reality. Two primary schools later emerged:123

• Academic Skepticism: Developed in Plato’s Academy during the 3rd century BCE, leaders like Arcesilaus and Carneades argued that certain knowledge is impossible, advocating instead for probabilistic standards.1
• Pyrrhonism: A later movement, associated with Aenesidemus and Sextus Empiricus, which criticized the Academics for claiming to know that "nothing can be known," instead utilizing tropes to challenge all dogmatic knowledge claims.1