This chapter offers a genealogy of the aesthetic categories ‘terror’ and ‘horror’ as they were constructed in eighteenth-century criticism. Drawing primarily upon authors such as John Dennis, Joseph Addison, Edmund Burke, Anna Laetitia Aikin, James Beattie, Nathan Drake and Ann Radcliffe, the chapter first establishes the common aesthetic and lexical ground shared by terror and horror early in the century, before tracing their increasing divergence during the formative years of the Gothic Revival. This aesthetic divergence, it is argued, is the culmination of a series of both explicit and implicit distinctions that consider various dimensions of fear, including the temporal, the moral, the degree of artifice, its relation to probability, and to gender. Critical discussion of these aesthetic categories is supplemented throughout by brief, illustrative examples from Gothic verse and fiction, some of which also expose the increasing politicisation of terror and horror in response to the French Revolution late in the century.