Studia Logica

, Volume 91, Issue 3, pp 383-406

First online:

Taking Degrees of Truth Seriously

  • Josep Maria FontAffiliated withDepartment of Probability, Logic and Statistics, Faculty of Mathematics, University of Barcelona Email author 

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This is a contribution to the discussion on the role of truth degrees in manyvalued logics from the perspective of abstract algebraic logic. It starts with some thoughts on the so-called Suszko’s Thesis (that every logic is two-valued) and on the conception of semantics that underlies it, which includes the truth-preserving notion of consequence. The alternative usage of truth values in order to define logics that preserve degrees of truth is presented and discussed. Some recent works studying these in the particular cases of Łukasiewicz’s many-valued logics and of logics associated with varieties of residuated lattices are also presented. Finally the extension of this paradigm to other, more general situations is discussed, highlighting the need for philosophical or applied motivations in the selection of the truth degrees, due both to the interpretation of the idea of truth degree and to some mathematical difficulties.


Suszko’s Thesis many-valued logic logical values truth values truth degrees logics preserving degrees of truth semantics abstract algebraic logic