One of the deepest and most ancient problems in philosophy is what we might call the problem of knowledge. There seems to be an unbridgeable gap between our abstract, complex, highly structured knowledge of the world, and the concrete, limited and confused information provided by our senses. Since the Meno, there have been two basic ways of approaching this problem, rationalism and empiricism. Each era seems to have its matched pair of advocates of each view, making their way through the centuries like couples in some eternal philosophical gavotte, Plato and Aristotle, Descartes and Locke, Leibniz and Berkeley, Kant and Mill. The rationalist approach says that although it looks as if we learn about the world from our experience, we don’t really. Actually, we knew about it all along. The most important things we know were there to begin with, planted innately in our minds by God or evolution (or chance). The empiricist approach says that although it looks as if our knowledge is far removed from our experience, it isn’t really. If we rearrange the elements of our experience in particular ways, by associating ideas, or putting together stimuli and responses, we’ll end up with our knowledge of the world. There is both a tension and a kind of complementarity between these two ideas,