In eighteenth-century Britain, philosophy was a broader subject than it is today and included many subjects covered elsewhere in this book, such as science, political theory, and theology. This chapter focuses chiefly on those eighteenth-century topics in philosophy that have most shaped present-day philosophical discussion. The first of these is epistemology or the theory of knowledge: the study of what we know and how we know. John Locke, David Hume, and Thomas Reid called this the study of the human mind or understanding. We will also consider another area where the contributions of eighteenth-century British philosophers are widely recognized today: the work in moral and ethical philosophy of a group of thinkers commonly called the ‘British moralists’. From the ancient Greeks and Romans, eighteenth-century thinkers inherited an understanding of philosophy as a way of life and a guide to living well. On what basis do we arrive at moral principles of right and wrong, and what motivates us to follow those principles in our actions: our reason or our feelings? These questions concerned such thinkers as Samuel Clarke, the earl of Shaftesbury, Francis Hutcheson, and Adam Smith.