Soft Deontic Logic

  • Txetxu Ausín
  • Lorenzo Peña
Part of the Studies in Fuzziness and Soft Computing book series (STUDFUZZ, volume 273)


Deontic logic is the theory of valid inference rules containing qualifications of prohibition, duty, or permission. Three main assumptions of standard deontic-logic approaches are here discussed and rejected: (1) the modal conception of deontic logic, according to which “licit” means “possible without breaking the rules”; (2) the gap between facts and norms, which contends that what actually happens has no bearing on duties; and (3) bivalence, which bars any situation inbetween absolute truth and downright falseness. As against such approaches, we put forward an alternative deontic logic we call soft, which, while being fuzzy (and based on a a paraconsistent gradualistic sentential calculus), binds duties to facts by espousing the implantation principle, according to which, if A is the case, then the duty (or permission) to do B – if – A implies the duty (or permission) to do B. By embracing degrees of licitness our proposal upholds a principle of proportionality ruling out deontic leaps. A formalized axiomatic system along those lines is developed.


Inference Rule Classical Logic Normative System Normative Reasoning Deontic Logic 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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© Springer-Verlag Berlin Heidelberg 2012

Authors and Affiliations

  • Txetxu Ausín
    • 1
  • Lorenzo Peña
    • 2
  1. 1.Unit of Applied Ethics at Spanish National Research Council (CSIC)MadridSpain
  2. 2.CSICMadridSpain

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