Epistemology is a characteristically modern field of philosophy, one where Cartesian or post-Cartesian scepticism plays a prominent role. One might thus raise legitimate concerns about the application of this term in connection with ancient philosophical literature. Ancient philosophers in general and the commentators in particular discussed various questions related to knowledge (epistēmē) and some of these questions resemble issues in today's epistemology. However, much of the commentators' discussion about knowledge or epistēmē is more akin to what we conceive of as philosophy of science: philosophical research into questions of what are the methods, limits, objects or aims of a systematic study into the world around us. We shall address these concerns in Chapter 3.

This chapter concentrates on the following questions: if there is knowledge, is it based on some starting-points that are known without proof? Are there different kinds of knowledge? Could we find starting-points for knowledge in perception? Given that perceptual conflicts exist, can we rely on our perceptions? If the same wind appears to me to be cold and to you to be warm, is it cold or warm? Or is it both cold and warm? If an apple turns from green to red, is it green or red? And, more generally, if we have knowledge, how should it be defined? In the ancient material, we do find lively debates centring on these kinds of questions.