In support of this understanding of the twentieth-century history, it is noteworthy how philosophical arguments in favour of physicalism began to appear from the 1950s onwards. Some of these arguments appealed explicitly to the causal closure of the physical realm (Feigl 1958, Oppenheim and Putnam 1958). In other cases, the reliance on causal closure lay below the surface. However, it is not hard to see that even in these latter cases the causal closure thesis played a crucial role.