Models: Measuring or Cognitive Instruments?

Abstract A number of authors (Morgan in: Morgan and Morrison (Eds.) Models as mediators, Cambridge University Press, Cambridge, 1999; Boumans in Philos Sci 72(5):850, 2005; Morison in Philos Stud 143(1):33–57, 2009; Massimi and Bhimji in Stud Hist Philos Modern Phys 51:71–81, 2015; Parker in Brit J Philos Sci 68(1): 273–304, 2017) have argued that models can be quite literally thought of as measuring instruments. I here challenge this view by reconstructing three arguments from the literature and rebutting them. Further, I argue that models should be seen as cognitive rather than measuring instruments, and that the distinction is important for understanding scientific change: Both yield two distinct sources of insight that mutually depend on each other, and should not be equated. In particular, we may perform the exact same actions in the laboratory but conceive of them entirely differently by virtue of the models we endorse at different points in time.