In A Philosophical Enquiry... Edmund Burke sets out to define the nature of beauty and sublimity, and establish an objective criterion for discussing aesthetics. His definition of beauty as rooted in pleasure and sexuality, and the sublime in pain and survival, aligned him with the empiricists John Locke and David Hume, as he replaced the metaphysics of Plato's aesthetics with a psychological and physiological perspective. According to Burke, the sublime and the beautiful are experiences that can be explained by biological and sensual factors; thus he proceeds to explain how smooth lines, sweet tastes and middle frequencies of sound can be considered beautiful, and the terror created by high mountains and dark forests can be sublime. These revolutionary ideas ushered in the age of Romanticism, and the Gothic genre of novels, with their delight in horror and fright, and continue to influence aesthetic theories today.