This Appendix has charted the history of changing attitudes to the completeness of physics. The important point is that a scientific consensus on completeness was reached only in the middle of the twentieth century. In earlier centuries there was no compelling reason to believe that all physical effects are due to physical causes, and few scientists did believe this. But by the 1950s the combination of the physiological evidence with the argument from fundamental forces left little room for doubt about the doctrine.
In Chapter 1 I raised the question of why philosophical physicalism is peculiarly a creature of the late twentieth century. I hope I have now succeeded in showing that this is no intellectual fad, but a reflection of developments in empirical theory. Without the completeness of physics, there is no compelling reason to identify the mind with the brain. But once the completeness of physics became part of established science, scientifically informed philosophers realized that this crucial premiss could be slotted into a number of variant arguments for physicalism. There seems no (p.256) reason to look any further to explain the widespread philosophical acceptance of physicalism since the 1950s.
Of course, as with all empirical matters, there is nothing certain here. There is no knock‐down argument for the completeness of physics. You could in principle accept the rest of modern physical theory, and yet continue to insist on special mental forces, which operate in as yet undetected ways in the interstices of intelligent brains. And indeed, there do exist bitter‐enders of just this kind, who continue to hold out for special mental causes, even after another half‐century of ever more detailed molecular biology has been added to the inductive evidence which initially created a scientific consensus on completeness in the 1950s. Perhaps this is what Tyler Burge has in mind when he says that ‘materialism is not established, or even deeply supported, by science’, or Stephen Clark when he doubts whether anyone could ‘rationally suppose’ that empirical evidence ‘disproves’ mind‐body dualism. If so, there is no more I can do to persuade them of the completeness of physics. However, I see no virtue in philosophers refusing to accept a premiss which, by any normal inductive standards, has been fully established by over a century of empirical research.