Fuseli’s painting The Nightmare delivers a rational explanation of the 18th century understanding of the influence on humans, and interconnections between, demons, superstition, and fantasy. At the same time it is an artistic interpretation of the instinct and the unconscious. Thus, Fuseli’s art combines both the scientific, rational understanding of phenomena, and the projection of imagination and emotion. Linked to this is the representation chosen by the artist of the interior being expressed by the exterior. With this work, Fuseli addressed the demands of the Enlightenment, to capture the spiritual empiricist, by reflecting the indivisible relationship between the soul and the body, while portraying the physiological and psychological understanding of that time. Another important influence on this work was the physiognomy of Johann Caspar Lavater. Fuseli found a new source of sensuality, and offered new subjects such as madness, melancholy, and fear of modern art, opening a road to Romanticism.