Jean-Marie Schaeffer, one of France's leading aestheticians, explores the writings of Kant, Schlegel, Novalis, Hegel, Schopenhauer, Nietzsche, and Heidegger to show that these diverse thinkers shared a common approach to art, which he calls the "speculative theory." According to this theory, art offers a special kind of intuitive, quasi-mystical knowledge, radically different from the rational knowledge acquired by science. This view encouraged theorists to consider artistic geniuses the high-priests of humanity, creators of works that reveal the invisible essence of the world. Philosophers came to regard inexpressibility as the aim of art, refused to consider second-tier creations genuine art, and helped to create conditions in which the genius was expected to shock, puzzle, and mystify the public. Schaeffer shows that this speculative theory helped give birth to romanticism, modernism, and the avant-garde, and paved the way for an unfortunate divorce between art and enjoyment, between "high art" and popular art, and between artists and their public.