This chapter discusses the theoretical connection between Hume’s arguments on imagination in theTreatise and opinion in Essays, Moral and Political, through which Hume’s keen awareness of the fragility of civilisation and the changeability of our social systems is elucidated. Although commentators have tended to base their understandings of Hume as a conservative thinker on his repeated emphasis on the importance of custom and habit to consolidate our beliefs, Hume’s anti-rationalism and emphasis on custom do not necessarily lead him to defend ‘tradition’ as such indiscriminately. Rather, his point lies in revealing that what is normally considered ‘tradition’ in fact consists of nothing but public opinion concerning what is thought to be established. This chapter will also reveal that this viewpoint is consistent with Hume’s criticism of the myth of the ancient constitution and social contract theory. This point is vital for our understanding of the ‘historical’ Hume, because some of his contemporaries criticised his History not only for his alleged Toryism, but also for his inconsistency with these earlier standpoints.