The mathematical turn in philosophy: measurement, computation, (de)idealization

• Applicant: Privatdozent Dr. Martin Fischer
• Subject Area: Theoretical Philosophy
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 566495555

We live in an era in which mathematics is employed in almost every academic discipline. Despite its traditional focus, philosophy is by no means exempt from this trend. This project provides a critical framework for addressing the increasing role of mathematics and computation in several of its core areas. The entanglement of mathematics with philosophy arises in two principal ways. The first is when mathematics is used to formulate philosophical claims, such as when real numbers are used to measure credences (degrees of belief), or when partial orderings are used to represent agents’ preferences. The second is when mathematics is used to derive philosophical conclusions, such as the use of Dutch book theorems in epistemology, or impossibility theorems like Arrow’s or Sen’s in political philosophy. But the use of these mathematical frameworks sometimes induces idealizations. For example, mathematical theory of probability tacitly assumes "logical omniscience": ideally rational agents are assumed to be able, when given any sentence, to determine whether it is a logical truth or not. Depending on the logic in question, this is either an infeasibly hard problem to compute (what computer scientists call NP-complete) or outright impossible (as hard as Turing’s halting problem). Even highly idealized or "artificially intelligent" agents are subject to these limitations. Our overarching objective is to develop a unified methodology for understanding the mathematical turn in contemporary philosophy. We aim to achieve this by employing a group of related methods from mathematical logic and computer science clustered around the subject known as reverse mathematics. These tools will be used to isolate the mathematical and computational principles required to sustain various philosophical arguments and theories via a novel method we call "§reverse philosophy". We investigate this concretely by investigating three interlinked case studies of the application of mathematics in philosophy: paradoxes of truth and vagueness, subjective probability in epistemology and artificial intelligence, and voting theory as applied to political philosophy.

• DFG Programme: Research Grants
• International Connection: United Kingdom
• Partner Organisation: Arts and Humanities Research Council
• Co-Investigator: Professor Dr. Hannes Leitgeb
• Cooperation Partners: Professor Dr. Walter Dean, Ph.D.; Professor Dr. Benedict Eastaugh