Knowing what would happen: The epistemic strategies in Galileo’s thought experiments Kristian Camilleri School of Historical and Philosophical Studies, University of Melbourne, Parkville, Victoria 3010, Australia article info Article history: Received 23 February 2015 Received in revised form 28 July 2015 Available online 24 August 2015 Keywords: Thought experiments; Galileo; Epistemic strategies; Rhetoric; Early modern science abstract While philosophers have subjected Galileo’s classic thought experiments to critical analysis, they have tended to largely ignored the historical and intellectual context in which they were deployed, and the specific role they played in Galileo’s overall vision of science. In this paper I investigate Galileo’s use of thought experiments, by focusing on the epistemic and rhetorical strategies that he employed in attempting to answer the question of how one can know what would happen in an imaginary scenario. Here I argue we can find three different answers to this question in Galileo later dialogues, which reflect the changing meanings of ‘experience’ and ‘knowledge’ (scientia) in the early modern period. Once we recognise that Galileo’s thought experiments sometimes drew on the power of memory and the explicit appeal to ‘common experience’, while at other times, they took the form of demonstrative arguments intended to have the status of necessary truths; and on still other occasions, they were extrapolations, or probable guesses, drawn from a carefully planned series of controlled experiments, it becomes evident that no single account of the epistemological relationship between thought experiment, experience and experiment can adequately capture the epistemic variety we find Galileo’s use of imaginary scenarios. To this extent, we cannot neatly classify Galileo’s use of thought experiments as either ‘medieval’ or ‘early modern’, but we should see them as indicative of the complex epistemological transformations of the early seventeenth century. Ó 2015 Elsevier Ltd. All rights reserved. When citing this paper, please use the full journal title Studies in History and Philosophy of Science. 1. Introduction Galileo is widely recognized as a masterful exponent of the use of thought experiment in science. His writings are replete with imaginary scenarios involving moving ships, falling stones and balls rolling down inclined planes. In 1969 Charles Schmitt noted, “the role of thought experiments” in Galileo’s early work, “as well as the more general problem of their changing function as Galileo developed from youth to maturity and adagedis a very important one which should be dealt with in detail” (Schmitt, 1969, p. 87). Yet, in spite of the prominent role that thought experiments assumed in Galileo’s writings, there has been relatively little detailed historical analysis of how they functioned in his science. Scholars have long recognised that thought experiments played an important rhetor- ical role in Galileo’s writings. Michel Segré, for example, argues that while Galileo did perform many concrete experiments, he often preferred to present his reader with “much simpler, “ideal” ex- periments”. In “presenting his science” to the reader, “Galileo put his trust more in thought experiments than in real ones” (Segré, 1980, p. 246). Yet the question of how Galileo attempted to persuade his reader of conclusions by means of the contemplation of imaginary scenarios is one that merits further attention. This paper attempts to address just this question, through an exami- nation of the different epistemic strategies that Galileo employed in his use of thought experiments, particularly in his later dialogues. Notwithstanding the important recent work of and Paolo Palmieri (2005) and Carla Rita Palmerino (2011), the general neglect of serious historical scholarship into Galileo’s use of thought experiments can be sharply contrasted with the fact that E-mail address: kcam@unimelb.edu.au. Contents lists available at ScienceDirect Studies in History and Philosophy of Science journal homepage: www.elsevier.com/locate/shpsa http://dx.doi.org/10.1016/j.shpsa.2015.08.009 0039-3681/Ó 2015 Elsevier Ltd. All rights reserved. Studies in History and Philosophy of Science 54 (2015) 102e112