The Historical Challenge to Realism and Essential Deployment

This chapter outlines how Deployment Realism resists Laudan and Lyons’s objections to the “No Miracle Argument” by arguing that a hypothesis is most probably true when it is deployed essentially in a novel prediction. Criticizing Psillos’s criterion of essentiality, Lyons argued that Deployment Realism must committed itself to all the actually deployed assumptions and concluded that the No Miracle Argument and Deployment Realism fail, since many actually deployed assumptions proved false. The chapter replies that an essentiality condition is required by Occam’s razor and that there is, in fact, a simpler formulation of essentiality that escapes Lyons’s criticisms and rescues the No Miracle Argument and Deployment Realism from their purported historical counterexamples: a hypothesis is essential when it has no proper parts (in Yablo’s sense) sufficient to derive the same prediction. The chapter concludes that, although essentiality so conceived cannot be detected prospectively, this is just natural, and it is not a problem but an advantage for Deployment Realism.