In modern epistemology, certain assumptions about knowledge are common, such as the view that the existence of knowledge must be justified against the sceptic. How does this differ from ancient philosophical ideas about knowledge? ‘Reason, knowledge and scepticism’ explores some of the strands of ancient thinking about knowledge, and lack of it by focusing on ancient thinkers such as Socrates and Plato. What emerges is the width and diversity of approaches. There are several ways to understand knowledge in ancient philosophy and engage not just with knowledge, but with problems of belief and the powers of positive and negative reasoning.