Distances between formal theories

Mohamed Khaled, Gergely Székely, Koen Lefever, Michèle Friend

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)


In the literature, there have been several methods and definitions for working out whether two theories are “equivalent” (essentially the same) or not. In this article, we do something subtler. We provide a means to measure distances (and explore connections) between formal theories. We introduce two natural notions for such distances. The first one is that of axiomatic distance, but we argue that it might be of limited interest. The more interesting and widely applicable notion is that of conceptual distance which measures the minimum number of concepts
that distinguish two theories. For instance, we use conceptual distance to show that relativistic and classical kinematics are distinguished by one concept only.
Original languageEnglish
Pages (from-to)633-654
Number of pages21
JournalReview of Symbolic Logic
Issue number3
Early online date4 Oct 2019
Publication statusPublished - Sep 2020


  • Logic
  • Definition Theory
  • Conceptual Distance
  • Philosophy of Science


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