 The role played by scientific theories within Salmon’s mechanistic view should not pass unnoticed. Both causal production and processes defined in terms of conserved quantities include an appeal to theories and laws of nature, because only “our current theories tell us what quantities to think of as conserved” (Salmon 1994b [1998: 258]). Similarly, to describe causal interactions one must appeal to laws such as the conservation of energy and momentum. This led Salmon to conclude: