Second, CTM offers an account of how a physical object (in particular, the brain) can produce rational thought and behavior. The answer is that it can do so by implementing rational processes as causal processes. This answer provides a response to what some philosophers—most famously Descartes , have believed: that explaining human rationality demands positing a form of existence beyond the physical. That is, it is a response to dualism (See Descartes 1637/1985, 139-40, and see Rey 1997 for discussion of CTM as being a solution to “Descartes’ challenge”). It therefore stands as a major development in the philosophy of mind.