Matt Brewer Dissertation Defense

Matt Brewer's Dissertation Defense. Open to members of the philosophy department. Title: "Towards a Philosophy of Plate Tectonics: Pluralism in Explanation, Evidence, and Classification" Abstract: This dissertation contributes to the traditionally neglected, but now rapidly growing, field of philosophy of the geosciences by providing a philosophical analysis of the many forms of pluralism that shape scientific practice in plate tectonics. Geoscientists studying plate tectonics face numerous epistemic challenges, but these challenges make the theory ripe for philosophical analysis. I examine three such epistemic challenges in the central chapters of this dissertation, and I argue that each challenge calls for a distinct form of scientific pluralism, which I assess for its methodological strengths and weaknesses. After introducing plate tectonics and motivating the philosophical relevance of the project in the first chapter, in chapter 2, I take a history of philosophy of science (HOPOS) approach to uncover a variety of different forms of scientific pluralism from the methodological writings of a key 19th century figure in the history of the geosciences, Thomas C. Chamberlin, whose work is largely unknown to philosophers of science. Although Chamberlin does not use the language of pluralism, I use his so-called Method of Multiple Working Hypotheses (and later variations on this method) as a foundation for articulating three varieties of scientific pluralism. In the subsequent chapters, I show how the three varieties of pluralism emerge within central debates in contemporary plate tectonics. I address the first debate in chapter 3, which concerns the role of mechanistic explanation in the rejection of continental drift and in the acceptance of plate tectonics, and how the mechanism(s) driving plate tectonics remain unresolved to this day. The epistemic challenge here is the inaccessibility of the interior of the Earth, and the different ways the mechanistic components of the processes driving plate tectonics can be carved up. The philosophical strategy that emerges is a nonintegrative explanatory pluralism, which I show to be compatible with metaphysical monism. In chapter 4, I turn to another scientific debate in plate tectonics: the timing of the onset of tectonic plate motion in the history of the Earth. The epistemic challenge here is the inaccessibility of deep time, as such, my discussion draws on recent work in the philosophy of the historical sciences. I argue that the debate about timing turns on a plurality of approaches to the nature of evidence, and specifically whether or not absence of evidence should be taken as evidence of absence. While the standard answer says “no,” I defend what I call a pragmatic approach to the absence of evidence, which is based in a pluralism about evidential standards. Is plate tectonics unique to Earth or does it occur on other planets or moons within our solar system and beyond? The epistemic challenge here is the inaccessibility of distant worlds, and it poses what I call in chapter 5 the “tectonic N = 1 Problem,” in analogy with the uniqueness of life on Earth. I argue that this issue also turns on how scientists choose to define plate tectonics, and how broadly or narrowly the classificatory categories are construed. For example, the movement of ice on Jupiter’s moon Europa satisfies some ways of defining plate tectonics, but not others. For the sake of making progress on this issue, I defend a classificatory or taxonomic pluralism. Finally, in a brief concluding chapter, I assess the project as a contribution to a novel “philosophy of plate tectonics,” summarizing the key scientific debates within plate tectonics and the many different forms of scientific pluralism they prescribe. I conclude by opening the door for future work drawing on another element of Chamberlin’s philosophy – pragmatism – in the project of developing a philosophy of the geosciences, of which this dissertation on the philosophy of plate tectonics is a part.