Abstract

Jean Perrin’s proof in the early-twentieth century of the reality of atoms and molecules is often taken as an exemplary form of robustness reasoning, where an empirical result receives validation if it is generated using multiple experimental approaches. In this article, I describe in detail Perrin’s style of reasoning, and locate both qualitative and quantitative forms of argumentation. Particularly, I argue that his quantitative style of reasoning has mistakenly been viewed as a form of robustness reasoning, whereas I believe it is something different, what I call ‘calibration’. From this perspective, I re-evaluate recent interpretations of Perrin provided by Stathis Psillos, Peter Achinstein, Alan Chalmers, and Bas van Fraassen, all of whom read Perrin as a robustness reasoner, though not necessarily in the same sort of way. I then argue that by viewing Perrin as a ‘calibration’ reasoner we gain a better understanding of why he believes himself to have established the reality of atoms and molecules. To conclude, I provide an alternative and more productive understanding of the basis of the dispute between realists and anti-realists. _1_ Introduction _2_ Perrin’s Reasoning: The Qualitative Argument _3_ Perrin’s Reasoning: The Quantitative Argument _4_ Perrin’s Realism _5_ Psillos, Achinstein, Chalmers, and van Fraassen on Understanding Perrin _6_ Conclusion