Abstract
According to many defenders of defeasible deontic logics, their systems provide an explanation of how conflicting norms are commonly processed, which standard deontic logic cannot offer because of its very nature. This is supposedly so for standard deontic logic is taken either (a) to rule out the very possibility of normative conflicts by validating the sentence “∼(Oa & O∼a)”, or (b) not to be able to offer any solution to normative conflicts. Against this twofold view, I argue, on the one hand, that standard systems of deontic logic are well capable of accounting for normative conflicts, by using the basic distinction between norms and propositions about norms. On the other hand, I argue that defeasibilist attempts to dealing with antinomies are in need of clarification: in fact, (1) on their descriptive reading, it is not clear in which stage of normative reasoning they locate conflict-solving activities; (2) on their normative reading, in turn, defeasibilist proposals of conflict-processing do not seem to be very promising, for they are either reducible to deductivist approaches or are not able to solve normative inconsistencies.
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Notes
- 1.
A personal anecdote may help: I can recall Jules Coleman lecturing at the Faculty of Law of the University of Toronto and summing up this turn in legal philosophy by means of a catch phrase: “Dworkin is Quine to Hart’s Carnap”.
- 2.
See Alchourrón (1993, 67).
- 3.
- 4.
- 5.
- 6.
See Hilpinen (1987, 37).
- 7.
“T” is for any tautology.
- 8.
This is one of the main arguments proposed by Horty (1997).
- 9.
“B” is for “bird”, “N” for “penguin”, and “F” for “flying”.
- 10.
A sentence with antecedent A is said to be more specific than a sentence with antecedent B, relative to a theory T, if we can derive all of B from A using only the sentences in T, but not vice versa.
- 11.
It is worth mentioning that, in the discussion of this problem, examples usually introduce other circumstances such as “x has a broken wing”, “x has its legs, or wings, tied up”, and so on. Now, it seems to me that there is a fundamental difference between the exceptions of penguins and the other mentioned exceptions. In the former case, what lacks is the dispositional property of “being able to fly”. This means that a certain individual, which pertains to the subspecies of penguins, cannot possibly be able to fly (they are not able to fly under any circumstances). In the other cases, what lacks is not the dispositional property of being able to fly, which does not characterize any subspecies, but a contingent feature of a possible (viz. not necessary and not impossible) state of affairs (for instance: birds with a broken wing are able to fly if they are cured and they have presumably flown before being injured). The same, with more reason, may be argued as for birds with tied-up wings. So, the revision of the antecedent of the universal referring to penguins ends with the introduction of the exception regarding the fact that penguins cannot fly, whereas the revision of the antecedent of universals regarding “birds with broken wings” or “birds with tied-up legs” can be endlessly revised due to contingent future facts (“Tweety is cured” or “Tweety’s legs have been untied”) which can materialize and trigger such a revision.
- 12.
- 13.
On the possible relations among the mentioned criteria, see Bobbio (113 ff.).
- 14.
Nute (1999, 216) admits that when more than one precedence criterion is taken into account, the relationships which can be envisaged among such criteria, and the defeasible or indefeasible treatment of them, are not easily depicted by a logical model. In this sense, defeasible deontic logics encounter, at a higher level, the same “problems” that classical deontic logic supposedly meet at a lower level.
- 15.
As Guastini (2010, 363 ff.) has shown, the criterion of speciality is commonly used to give a more specific norm priority over a more general one, but it is also used, sometimes, to give alternative priority to one of two rules which connect incompatible solutions to only a subset of the cases which are referred to in their antecedents. The chronological principle is used to cancel ex nunc the validity of a norm N1 which has been enacted before norm N2, which has the same hierarchical level as N1 and attaches an incompatible solution to the same set or subset of the cases referred to in the norms’ antecedents. Finally, the hierarchical principle is used to solve antinomies between norms of different hierarchical levels, by invalidating ex tunc the inferior norm.
- 16.
As is widely known, this is, among others, Kelsen’s as well as Dworkin’s view. Cf. Ratti (2008, part I).
- 17.
The main one is, no doubt, the one elaborated by Alchourrón-Makinson (1981). See also Alchourrón-Bulygin (1981). Perhaps, it is worth recalling that this was one of the main stages to the elaboration of AGM theory (which was already noted on p. 147 of Alchourrón’s and Makinson’s paper), whose relevance for AI and nonmonotonic reasoning is richly explained in Carnota-Rodríguez (2006, 9 ff.). The analysis provided by Carnota and Rodríguez shows the genesis of Alchourrón’s ideas on the topic (from legal theory to beliefs change) and how his works were fundamental in establishing this field of research.
- 18.
For this reason, it is very surprising that Royakkers-Dignum (1997, 263) ascribe Alchourrón’s and Makinson’s model to defeasible reasoning. This misattribution is probably due to a labelling problem: as mentioned in the text, there is a tendency to call “defeasible logics” those which deal with the problem of conflicts of norms.
- 19.
As a matter of fact, the very “nature” of defeasible logics is controversial. Cf. for instance the following passage from Morado (2004, 324) where many of the typical characterizations of defeasible logic are impugned: “Defeasible reasoning is not necessarily an irrational pattern, nor does it require wrong conclusions or insecure premises. It is an inference which depends on the context and thus may be blocked. Moreover, it does not follow from the fact that rules are revisable (indeed, the majority of scientific rules are such), nor from the fact that it has tacit premises”.
- 20.
See Bulygin (1986). In Ratti (2008), Bulygin’s model is refined and eleven different operations usually carried by jurists are singled out and analysed. Here it is important to stress that further action—i.e. application of a general rule to a given case—is typically carried out by judges, but not by commentators.
- 21.
See Ferrer Beltrán-Ratti (2010).
- 22.
An analogous idea has been formulated with a catch phrase by Morgan (2000, 347), whose analysis is concerned primarily with ordinary, and not legal, reasoning: “The nonmonotonicity of commonsense reasoning is due to the way we use logic, and not due to the logic that we use”.
- 23.
For discussion, see Tur (2001).
- 24.
Cf. the seminal Ross (1945).
- 25.
See Nute (1999, 216–217).
- 26.
From a strictly logical point of view, it must reject at least one of the following rules: the rule for introducing the disjunction, the principle of monotony, the disjunctive syllogism, or the rule of cut. This is so because such rules conjunctively imply the ex falso quodlibet principle. For discussion, see Alchourrón (2010, 75).
- 27.
This is Dworkin’s view, as I have tried to show in Ratti (2008, 143–173).
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Ratti, G.B. (2013). Normative Inconsistency and Logical Theories: A First Critique of Defeasibilism. In: Araszkiewicz, M., Šavelka, J. (eds) Coherence: Insights from Philosophy, Jurisprudence and Artificial Intelligence. Law and Philosophy Library, vol 107. Springer, Dordrecht. https://doi.org/10.1007/978-94-007-6110-0_6
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