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Reasoning with Rules and Rights: Term-Modal Deontic Logic

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Part of the book series: Logic, Argumentation & Reasoning ((LARI,volume 23))

Abstract

General obligations such as ‘every driver has to give way to a driver coming from the right’ are central in legal reasoning, but have been mostly overlooked in deontic logic. We claim that a simple extension of Standard Deontic Logic to the predicative level is insufficient to capture general obligations. Instead, we argue for an explicit representation of bearers (and counterparties) of obligations as terms in a quantified deontic logic. To achieve this we develop a term-modal counterpart of Standard Deontic Logic and give a sound and strongly complete axiomatization for it. We go on to show that this logic is not only suitable for capturing reasoning with general obligations, but also with (multital and paucital) Hohfeldian rights relations and rules of rights.

The research on this paper was enabled by subventions from the Research Foundation—Flanders, through the project “Towards a more integrated formal account of actual ethical reasoning, with applications in medical ethics.” (G0D2716N). The authors are indebted to Thijs De Coninck, Federico Faroldi, Pawel Pawlowski, and Nathan Wood for comments on an earlier version of this paper. Frederik Van De Putte is a Marie Skłodowska-Curie Fellow at the University of Bayreuth and a Postdoctoral Fellow of the Research Foundation—Flanders.

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Notes

  1. 1.

    In legal reasoning, deriving consequences from general statements is not restricted to simple applications of so-called legal syllogisms. In view of the legal principle “like cases should be treated alike”, it is commonly accepted that all legal decisions should be founded on general rules (see, for instance, Feteris 2017, p. 25).

  2. 2.

    Within a logical approach to legal reasoning, logical validity is seen as a necessary requirement for the acceptability of legal arguments, see Feteris (2017), p. 25.

  3. 3.

    Achen et al. (2019) also uses a Hilbert-style axiomatisation.

  4. 4.

    A notable exception to the limitation to paucital rights is Markovich (2020).

  5. 5.

    There is no consensus in the literature on the terminology. Therefore our use of terminology might differ slightly from that found in other work.

  6. 6.

    We have in mind what is sometimes called ‘weak’ permission (Herrestad and Krogh 1995, p. 464). Logics of other notions of permission have been developed in recent work, cf. Hansson (2013). We leave the investigation of such notions in combination with term-modal logic for future work.

  7. 7.

    Herrestad and Krogh claim that they have “few clear and convincing intuitions” regarding directed permissions and argue that directed permissions are not the duals of directed obligations (Herrestad and Krogh 1995, p. 504).

  8. 8.

    “Elke bestuurder moet voorrang verlenen aan de bestuurder die van rechts komt, behalve indien hij op een rotonde rijdt of indien de bestuurder die van rechts komt uit een verboden rijrichting komt.” Artikel 12.3.1. van het Koninklijk besluit houdende algemeen reglement op de politie van het wegverkeer en van het gebruik van de openbare weg.

  9. 9.

    See Van De Putte et al. (2019), Horty (2012), and Beirlaen (2018) for combinations of non-monotonic logic and deontic logic.

  10. 10.

    In all of our citations we will change the notation used for constants and variables (ranging over persons) to ensure a uniform notation and easy reading experience. We will use a, b, … for individual persons and x, y, … for variables ranging over persons.

  11. 11.

    The emphasis in this and further quotations is Hohfeld’s own.

  12. 12.

    The full quote is “A has an indefinite number of legal privileges of entering on the land, using the land, harming the land, etc” (Hohfeld 1917, p. 746). The phrase ‘indefinite number of privileges’ refers to an indefinite number of privileges to enter on the land, an indefinite number of privileges of using the land, etc. This is illustrated by the fact that Hohfeld later refers to these privileges as “multital, or in rem, ‘privilege-no-right’ relations” (Hohfeld 1917, p. 747).

  13. 13.

    Kanger’s theory of ‘atomic types of rights’ differs from the Hohfeldian theory of rights, but the point about the existence of ‘rules of rights’ holds regardless of the specific theory of rights one accepts.

  14. 14.

    Going even further: “A few states have held that in narcotics cases knowledge is not an essential element of possession” (Whitebread and Stevens 1972, p. 753).

  15. 15.

    Whether such a law is just is a different discussion.

  16. 16.

    Cfr. also Hohfelds indefinite classes of multital rights (Hohfeld 1917, p. 718).

  17. 17.

    This problem was already noted by Hansson (1970).

  18. 18.

    Equivalently, one can obtain constant domain semantics by assigning the same domain to every world.

  19. 19.

    It is also possible to expand the domain to also include other objects, like the apples from the introduction. See for example Achen et al. (2019).

  20. 20.

    Note that \(\{{\mathsf {O}}_a^b \varphi , {\mathsf {O}}_a^c \neg \varphi \}\) is inconsistent in TMDL, but not in this new logic.

  21. 21.

    For conflict-tolerant deontic logic, see Van De Putte et al. (2019) and Goble (2013).

  22. 22.

    The converse is not valid.

  23. 23.

    This asymmetry was also noted by Hohfeld, see Sect. 13.3.

  24. 24.

    Note that Hohfeld himself also laments the fact that there is no single term available to express the correlative of a permission (Hohfeld 1913, p. 33).

  25. 25.

    A broad class of non-normal, classical term modal logics is studied in Frijters and Van De Putte (2020).

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Correspondence to Stef Frijters .

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Frijters, S., Meheus, J., Putte, F.V.D. (2022). Reasoning with Rules and Rights: Term-Modal Deontic Logic. In: Rahman, S., Armgardt, M., Kvernenes, H.C.N. (eds) New Developments in Legal Reasoning and Logic. Logic, Argumentation & Reasoning, vol 23. Springer, Cham. https://doi.org/10.1007/978-3-030-70084-3_13

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