Object-Based Unawareness: Axioms

Oliver J. Board, Kim Sau CHUNG

Research output: Contribution to journalArticlepeer-review


This paper provides foundations for a model of unawareness, called objectbased unawareness (OBU) structures, that can be used to distinguish between
what an agent is unaware of and what she simply does not know. At an informal
level, this distinction plays a key role in a number of papers such as Tirole
(2009) and Chung & Fortnow (2016). In this paper, we give the model-theoretic
description of OBU structures by showing how they assign truth conditions to
every sentence of the formal language used. We then prove a model-theoretic
sound and completeness theorem, which characterizes OBU structures in terms
of a system of axioms. We then verify that agents in OBU structures do not
violate any of the introspection axioms that are generally considered to be
necessary conditions for a plausible notion of unawareness. Applications are
provided in our companion paper.
Original languageEnglish
Pages (from-to)1-36
Number of pages36
JournalJournal of Mechanism and Institutional Design
Issue number1
Publication statusPublished - Dec 2021

User-Defined Keywords

  • Awareness
  • object-based unawareness
  • modal logic


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