The Greek word skepsis means investigation. By calling themselves skeptics, the ancient skeptics thus describe themselves as investigators. They also call themselves ‘those who suspend’ (ephektikoi), thereby signaling that their investigations lead them to suspension of judgment. They do not put forward theories, and they do not deny that knowledge can be found. At its core, ancient skepticism is a way of life devoted to inquiry. Also, it is as much concerned with belief as with knowledge. As long as knowledge has not been attained, the skeptics aim not to affirm anything. This gives rise to their most controversial ambition: a life without belief.
Ancient skepticism is, for the most part, a phenomenon of Post-Classical, Hellenistic philosophy. The Academic and Pyrrhonian skeptical movements begin roughly in the third century BCE, and end with Sextus Empiricus in the second century CE. Hellenistic philosophy is a large-scale conversation, not unlike philosophy today. The skeptics (among them Pyrrho, Timon, Arcesilaus, Carneades, Aenesidemus, and Sextus Empiricus) do engage with Pre-Socratic philosophy, Socrates, Protagorean relativism, Plato, and perhaps Aristotle. But their contemporary and principal interlocutors are Epicureans, Stoics, Cynics, and Megarian logicians (cf. Long 2006, ch. 4 and 5).