Speaker
Jeremy Seligman

Abstract
A definition formulated correctly using necessary and sufficient conditions introduces new vocabulary via an interpretation in a familiar language. A recursive definition introduces the application of vocabulary to new objects in terms of previously understood applications to other, typically less complex, objects. A circular definition, such as the definition of truth that plagues our attempts to understand self-referential truth claims, may change the predicate that it defines. In this talk, I will reflect on a conception of definitions as dynamic operators. This includes the approach to relation-change dynamics introduced in [1] and studied algebraically in [2].

[1] P. Girard, J. Seligman and F. Liu. General dynamic dynamic logic. In S. Ghilardi T. Bolander and L. Moss, editors, Advances in Modal Logic, volume 9, pages 239–260. College Publications, 2012.
[2] M. Ma and J. Seligman. Algebraic semantics for dynamic dynamic logic. In W. van der Hoek, W. Holliday and W. Wang, editors, Logic and Rational Interaction (LORI 5), pages 255-267. Springer, 2015.