One of the most defining features of Rene Descartes’ philosophy is the nature and degree of his dualism. As conventional readings go, Descartes neatly divides reality into two radically distinct types of substances—mind and body—and never the two shall meet. I argue, however, that Descartes does not split the mind from body as cleanly as conventional readings might think, that the two metaphysical hemispheres are not entirely separate. There is a bridge linking the two together, and the road map for discovery is found in Descartes’ theory of sensory perception.
Descartes’ views on sensory perception is the most apt topic in which to seek an understanding of the relationship between mind and body because, in general, it requires some explanation about how immaterial souls are informed by material bodies; that is, the topic demands that Descartes hypothesize about how perceptions—which he considers exclusive to minds—can be of things wholly distinct in kind, things that are essentially material. Throughout his writings, Descartes pays most attention to visual sensory perception, and so I follow in suit. Moreover, I concentrate on visual shape perception because, as I argue, understanding this aspect of Descartes’ philosophy leads to insights about the precise relationship between mind and body.
To give a feel for the overall shape of my reading, consider “veil of perception” interpretations of Descartes. Such readings understand Descartes as wedging a “third thing” between perceivers and the perceived object, standardly ascribing the “third thing” to the mind itself. On such readings of Descartes, sensory access to the physical world is mediated by mental images. So, according to these readings, one sees an idea of a tree, but not the tree itself. According to the reading of Descartes I offer, however, the veil is sheerer than previously thought. For I argue that the “third thing” bridging perceivers with the perceived belongs to bodily substance. In particular, I argue that minds directly perceive a part of the brain. This view has ramifications for Descartes’ dualism because, in order to make sense of exactly how minds are directly aware of their brain, Descartes posits a unique ontological item shared between mind and body, thereby rejecting the absolute dualism supposed by more conventional readings.
My arguments for these claims rely chiefly on interpreting Descartes as adhering to the presentation thesis, a thesis claiming, in general, that minds directly attend to a brain state. The first three chapters of the dissertation are devoted to showing how the presentation thesis fits with and can be derived from the full range of Descartes’ writings. In the final chapter I argue that the presentation thesis influences Nicolas Malebranche, in part, to locate the “wedge” of his theory of sensory perception in God.
Keywords: Descartes, Malebranche, Pineal Gland, Vision, Vision in God, Optics, Early Modern Philosophy, Causation, Primary and Secondary Quality Distinction, Visual Perception, Sensory Perception, Sensation