  To understand why this scholium is so important, it is helpful to recall Descartes’ definition of a “real distinction.” In the Principles of Philosophy, Descartes says: “Strictly speaking, a real distinction exists only between two or more substances; and we can perceive that two substances are really distinct simply from the fact that we can clearly and distinctly understand one apart from the other” (Principles, I, §60, CSM, I, p. 213, AT 28). For Descartes, this anchors the strict epistemological and ontological separation between mind and body. One of the things we learn from going through the Meditations is that we are capable of clearly and distinctly perceiving ourselves without a body—the cogito in the Second Meditation, and we clearly and distinctly perceive body without thinking in the Fifth Meditation. (Of course, in retrospect, we realize that we already did this in a sense with the wax as well). Descartes thus concludes that mind and body are really distinct, that is, one can exist without the other.