Journal of Philosophical Logic

, Volume 42, Issue 4, pp 635-641

First online:

An Intuitionistic Reformulation of Mally’s Deontic Logic

  • Gert-Jan C. LokhorstAffiliated withSection of Philosophy, Faculty of Technology, Policy and Management, Delft University of Technology Email author 

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In 1926, Ernst Mally proposed a number of deontic postulates. He added them as axioms to classical propositional logic. The resulting system was unsatisfactory because it had the consequence that A is the case if and only if it is obligatory that A. We present an intuitionistic reformulation of Mally’s deontic logic. We show that this system does not provide the just-mentioned objectionable theorem while most of the theorems that Mally considered acceptable are still derivable. The resulting system is unacceptable as a deontic logic, but it does make sense as a lax logic in the modern sense of the word.


Deontic logic Intuitionistic logic Lax logic