Sometime in the early 1620s young Rene Descartes came across Johannes Kepler’s Optical Part of Astronomy. From that point on, his epistemological project was predicated on the fundamental insight of Kepler’s new optics: that the eye is not a window but a screen; that it does not provide re-presentations of the objects but merely records the effects of physical process. Descartes’ first attempts to redress this blow to traditional epistemology by ascribing human knowledge with divine-like vision—intuition. When this fails, he turns to apply to knowledge the same naturalizing tools of the New Science that created the conundrum. Sensations are causal effects, he explains in the Meditations, and it is the causal order of nature that warranties their validity. This was the way he was understood by his more sophisticated contemporaries: the challenge presented by Descartes’ optics, explained Thommas White, Kenelm Digby and Joseph Glanvill, was to re-instate meaning into the purely physical sense perceptions. Each approached the challenge differently, but all agreed that the infamous rift between mind and world was not between body and soul, but between the two sides of the screen of the eye – the material world and the material brain. All agreed that Descartes’ immaterial soul was not the cause of the rift, but a (clumsy) attempt to resolve it: Descartes believed that he required such an entity to decipher the meaningless effects of the physical sensations.