Leibniz took the apparent correspondence between the mental and physical realms to be an act of God, a divinely “pre-established harmony.” In particular, he may have had in mind the correspondence between mathematics and the physical sciences. Physicist Eugene Wigner would later call this harmony “the unreasonable effectiveness of mathematics.” We do marvel even today at the effectiveness of mathematics to model nature. But perhaps the true marvel is the general ability of thought to model the external world at all. After all, there seems to be a correspondence, if not perfect, between sensory perception and reality. This suggests a harmony between world and brain, between ordinary cognition and natural reality. This does not mean that the world is as we see it, or that perception is an open window on the world, only that how we see it facilitates (or at least permits) our survival. Without a roughly reliable correspondence we simply would not be here. It means that the correspondence was built in by evolution through natural selection, through long experience over many generations. The world is obviously suitable for life, since here we are. Very likely it is intelligible for the similar reasons. Embodied participation in an evolutionary contest “pre-establishes” the relations between brain and world, including our very categories of thought. To the degree that logic reflects and abstracts cumulative actual experience, it is to be expected that logical truth should correspond to physical truth. Yet, science seeks out new realms of experience—or, rather, realms that cannot be directly experienced with the senses at all! The fundamental correspondence between mathematics and physical reality remains mysterious because it often holds in applications far removed from ordinary experience. However, a qualifying fact should be kept in mind: the systems investigated as “physical reality” are actually deductive systems—models. That is, physical reality has been re-defined in terms that lend themselves to mathematical expression. On that account, the pre-established harmony is less surprising.