J. Horty. Moral Dilemmas and Nonmonotonic Logic. In Proc. of the First International Workshop on Deontic Logic in Computer Science, Amsterdam, The Netherlands, 1991.  Home/Search   Document Details and Download   Summary   Related Articles   Check

....jR) entailed U , so too would R, D, I(U jR) and I(U jR D) Defeasible conditional preferences could not be expressed. Various logics have been proposed to capture factual detachment in the deontic setting, and recently several complex default reasoning schemes have been applied to this problem [18, 20]. We propose a simple solution based on the following observation: to determine preferences based on certain actual facts, we consider only the most ideal worlds satisfying those facts, rather than all worlds satisfying those facts. Let KB be a knowledge base containing statements of conditional ....

John F. Horty. Moral dilemmas and nonmonotonic logic. J. of Philosophical Logic, 1993. To appear.

....approaches to the logic of deontic, and in general defeasible, conditionality are restricted to unnested conditionals. In the AI Law field this arises as a consequence of the fact that current non monotonic or defeasible formalisms treat conditional obligation as a normal default (see e.g. [Hor94,Mak94,Pra93,TvT94]) However, perfectly understandable examples of nested conditionals occur both in ordinary language and in legal contexts. For example, judicial reasoning makes often use of the weak MP formula (A (A B) B to detach B in circumstances in which A and A B hold without known defeating ....

J. F. Horty. Moral dilemmas and nonmonotonic logic. Journal of Philosophical Logic, 23: 35--66, 1994.

....in the study of norms and normative reasoning. Defeasible reasoning methods have been proven to be able to cope with a variety of important issues. A number of di#erent approaches to formalizing defeasible deontic reasoning have been proposed and several frameworks have been exploited (see e.g. [1, 2, 3, 4, 5, 6, 7]) It turns out, however, that not much e#ort to account for deontic defeasibility in a computationally oriented manner has been made until now. This can partly be traced to the fact that usual nonmonotonic reasoning methods are not well suited to computational treatment. On the other hand, it has ....

....P p) and according to preference P 2 (which gives preference to Italian law) he cannot be poligamous (P 2 p) Let us finally consider an example which clearly involves not only a conflict, but also the need to choose between di#erent preferences. Example 5. 3 A question about table manners [2] 1a. A person must use knife and fork when eating. 2a. A person must not use knife and fork when eating asparagus. 3a. A person is eating asparagus. This set is translated into P 1 OT f a P 2 OTf a. In such a case we need to add to our system a mechanism for comparing preferences. ....

Horty J.F. Moral Dilemmas and Nonmonotonic Logic. Journal of Philosophical Logic 1994; 23: 35--65.

....if the overriding obligation is itself overridden, then with obligations under uncertainty there is no reinstatement, but with prima obligations there is. In the following de nition of obligations under uncertainty that does not satisfy reinstatement we use a simple de nition of overridden [30,31,64]. De nition 7 (Obligations under uncertainty) Let N be a set of contextual obligations of CDL. The set of derived factual independence statements of N is: F I(N) f ( j ) j ) j ( j ) 2 N is not overridden for g where ( j ) 2 N is overridden for if there is a ( ....

J.F. Horty. Moral dilemmas and nonmonotonic logic. Journal of Philosophical Logic, 23:35-65, 1994.

....situation (although there are physically possible in other circumstances) Note that since hDS;BKi is generally not complete, wP is generally not complete either. Thus there may be several incomparable preferred decisions. 4.3. Examples The following example illustrates an instance of what Horty (Horty, 1994) calls overridden rules. EXAMPLE 14. asparagus) 1.If you are invited to a dinner you should not eat with your ngers 2.If you are served asparagus you should eat with your ngers; 3.Being served asparagus means that you are invited to a dinner; aamas.tex; 30 05 2000; 14:52; p.31 32 4.You ....

.... and Tan, 1999a) for a survey) O(bja) holds i b holds in all preferred a worlds (Hansson, 1971) Dyadic deontic logics were developed to handle so called contrary toduty (CTD) obligations (see Examples 8, 12, 14, 17, 18) Defeasible obligations are handled in a non monotonic framework by Horty (Horty, 1994; van der Torre, 1994) Alternative approaches to the handling of CTD obligations were proposed by Prakken and Sergot (Prakken and Sergot, 1996) by Cholvy and Cuppens (Cholvy and Cuppens, 1995) who make use of roles ranked by a priority ordering assumed to be given note that our approach could ....

Horty, J.: 1994, `Moral Dilemmas and Nonmonotonic Logic'. Journal of Philosophical Logic 23, 35-65.

.... iterative approaches [vdTT99d, Mak99, MvdT99, vdT99a] are natural successors and generalizations of several approaches based on complex inductive definitions that recently have been proposed, usually applying techniques developed in non monotonic reasoning, such as Horty s non monotonic approach [Hor93, Hor94, vdT94] based on Reiter s default logic (Reiter s default rules do not have a truth value either and they iteratively construct extensions) Prakken and Sergot s contextual reasoning [PS96, PS97, vdTT99a, vdT99b] labeled deontic logic [vdTT97] and phased deontic logic [TvdT96] 2.3 Dilemmas A dilemma ....

J.F. Horty. Moral dilemmas and nonmonotonic logic. Journal of Philosophical Logic, 23:35--65, 1994.

....form: someone who is told not to kill must surely be able to infer that he or she ought not to kill by strangling, say. Yet another option is to reject the D scheme, a move which has also been suggested for other reasons, viz. as a way to represent moral dilemmas in a meaningful way (cf. e.g. (Horty, 1994)) However, as one of us has defended in (Prakken, 1996) we feel that that aim is better served by embedding a deontic logic validating the D scheme in some suitable non monotonic logic. In such a logic contradictions do not necessarily trivialise the premises, and thus they provide a way to ....

....Jones and P orn, 1985) do not use non monotonic techniques. However, this is perhaps because at the time non monotonic logics were not yet (widely) available. Since this has changed, the view that reasoning with prima facie obligations is non monotonic has become increasingly popular; see e.g. (Horty, 1994; Morreau, 1994; Prakken, 1996) Are contextual obligations prima facie obligations So then, are contextual obligations prima facie obligations From our discussion it follows that if they are, then they should satisfy some form of defeasible factual detachment: from it ought to be that A given ....

Horty, J. F. (1994). Moral dilemmas and non-monotonic logic. Journal of Philosophical Logic 23:35--65.

....between ideal and actual obligations is a satisfactory formalization of CTD reasoning. 2. 5 Defeasible and Contextual Deontic Logic (DDL, CDL) The last decade several defeasible deontic logics have been proposed, that formalize reasoning about obligations which are subject to exceptions [Hor94, Hor93, Jon93, vdTT95, Mor96, vdTT97b, NY97] It can be argued that most PDL s are DDL s, because they typically formalize obligations that do not have weakening (of the consequent) Jen85] or defeasible conditionals, i.e. conditionals that do not have strengthening of the antecedent [Alc93] In ....

....consequent, which derives S j= O Cdl (tj n :a) from the latter obligation. CDL is monotonic. The defeasibility can be made explicit when we define a variant of factual detachment for contextual obligations analogous to the construction of extensions in Reiter s default logic, see [Rei80, Hor93, Hor94] If :a is true, then Ot cannot factually be detached from O(tj n:a) but it can as long as the truth value of a has not been settled. 2.6 Temporal and Action Deontic Logic (TDL, ADL) Since the late seventies, several temporal deontic logics and deontic action logics were introduced, which ....

J.F. Horty. Moral dilemmas and nonmonotonic logic. Journal of Philosophical Logic, 23:35--65, 1994.

....i, M;w 1 j= ff i fi i and M;w 2 j= ff i fi i . We look for fl 1 and fl 2 such that: 8fl 1 ; fl 2 i2N (ff fi fl 1 ff i fi i ) ff fi fl 2 :ff i fi i ) or 6 9fl 1 ; fl 2 i2N (ff fi fl 1 : ff i fi i ) ff fi fl 2 : ff i fi i ) 9 Related research The work of Horty [Hor94, Hor93] can be related to our work. ns is like hD;W i defaults do not have a truth value deriving defaults from a set of defaults Horty: NS is set O(ffjfi) Inference relation fO(ff i jfi i ) j i = 1 : ng O(ffjfi) Veltman s normally presumably operators are closely related to the two deontic ....

J.F. Horty. Moral dilemmas and nonmonotonic logic. Journal of Philosophical Logic, 23:35--65, 1994.

.... E ] where Cn[S] is the consequence set of S. Example 2 Reconsider the deontic context of the previous example. E contains only a 1 and the conditioned extension E contains all logical consequences of a 1 a 2 . Horty shows that every deontic context has at least one extension. He also shows [4] [3] that this defeasibility approach can deal with conflicting obligations, for which he applies amethod of Van Fraassen [10] He benefits from the existence of multiple extensions when there are conflicting obligations, where every extension contains a maximal number of consistent obligations. ....

J.F. Horty, `Moral dilemmas and nonmonotoniclogic', Journal of Philosophical Logic, 23, 35--65, (1994).

....what seem to be genuine conflicts of obligations, arising from general prima facie principles, whereas D is taken to mean that such genuine conflicts do not exist. Various modal deontic logics have been proposed in which D is invalid but D valid ( 2, 26, 16] but, as argued by Horty in [8, 9, 10], these logics seem to be too weak. Consider, for example, You should either serve in the army or do alternative service and You ought not to serve in the army : intuitively, this seems to imply You should perform alternative service , but in all proposed logics without D also the scheme ....

....terms. 2 Horty s nonmonotonic deontic logic 2. 1 The logic One of the best known formalisations of nonmonotonic reasoning is Reiter s [24] default logic; this is the system used by Horty in developing his nonmonotonic deontic logic, which in turn is inspired by his logical reconstruction in [8, 10] of a proposal of van Fraassen [3] First I give a very brief outline of default logic (using the (F; Delta) notation of [22] It is based on a set F of first order formulas and a set Delta of defaults, which are inference rules of the form A : B=C, in which A is the prerequisite, B the ....

J.J. Horty, Moral dilemmas and nonmonotonic logic. Journal of Philosophical Logic 23 (1994), 35-65.

....what seem to be genuine conflicts of obligations, arising from general prima facie principles, whereas D is taken to mean that such genuine conflicts do not exist. Various modal deontic logics have been proposed in which D is invalid but D valid ( 2, 26, 16] but, as argued by Horty in [8, 9, 10], these logics seem to be too weak. Consider, for example, You should either serve in the army or do alternative service and You ought not to serve in the army : intuitively, this seems to imply You should perform alternative service , but in all proposed logics without D also the scheme ....

....researchers have advocated the use of nonmonotonic logics (see e.g. 4, 5] and, for an overview, 20] In [22, pp. 331 2] I have, moreover, suggested to apply this view to the issue of moral dilemmas and prima facie obligations. Horty s proposal is included in the same DeltaEON 91 proceedings ([8]) there he also presents a first formalisation involving deontic operators. Although thus the starting points of my suggestion and Horty s analysis are the same and although, moreover, both are based on Reiter s [24] default logic, there is an important difference. While the logic developed by ....

[Article contains additional citation context not shown here]

J.F. Horty, Moral dilemmas and nonmonotonic logic (preliminary report) . Proceedings of the First International Workshop on Deontic Logic and Computer Science, Amsterdam 1991, 212-231.

....(see [3] Conditional obligation forms the subject of a long standing and increasingly sophisticated tradition in modal logic, begun in the first half of this century by Georg H. von Wright (see [84] The more recent forms of this study draw on ideas from nonmonotonic logic (see [54] and [55]) The artificial intelligence literature offers a corresponding argument based approach to decision making, in which reasoning identifies explicit reasons for alternatives, for generic preferences and for other elements of decision formulations. These explicit reasons themselves may enter into ....

J. F. Horty. Moral dilemmas and nonmonotonic logic. Journal of Philosophical Logic, 23(1):35--65, 1994.

....can be overridden by stronger obligations. For example, you should keep your promises, but one may break a promise in order to prevent a disaster (Ross, 1930) normally you should not eat with your fingers, but if you are served asparagus, then normally you should eat with your fingers (Horty, 1994), normally there should not be a fence, but if the house in next to a cliff then normally you should have a fence (Prakken Sergot, 1996) etc. Dilemmas: conflict defeasibility. Horty (1994; 1997) gives a normative interpretation of Reiter s default logic, which is used to analyze dilemmas. ....

....your fingers, but if you are served asparagus, then normally you should eat with your fingers (Horty, 1994) normally there should not be a fence, but if the house in next to a cliff then normally you should have a fence (Prakken Sergot, 1996) etc. Dilemmas: conflict defeasibility. Horty (1994; 1997) gives a normative interpretation of Reiter s default logic, which is used to analyze dilemmas. He shows formal links between Reiter s default logic and Van Fraassen s analysis of dilemmas (van Fraassen, 1973) Unresolved conflicts: conflict defeasibility. Related to dilemmas is the issue ....

Horty, J. 1994. Moral dilemmas and nonmonotonic logic. Journal of Philosophical Logic 23:35--65.

....for defining a notion of consequence in the presence of multiple exten Note that this objection is directed only against the use of modal operators to capture the epistemic interpretation of default logic. Other interpretations, involving other modal operators, are possible; it is shown in [4], for example, that a deontic interpretation, with default conclusions wrapped inside of deontic operators, generates a logic for normative reasoning corresponding to that originally suggested by van Fraassen [16] sions, only the third, skeptical proposal endorse a conclusion whenever it is ....

John Horty. Moral dilemmas and nonmonotonic logic. Journal of Philosophical Logic, 23:35--65, 1994.

....brave and cautious reasoning. 32 3 Reiter provides a proof procedure, sound and complete under certain conditions, for determining whether a formula is believable in this sense on the basis of a default theory. A di erent interpretation of this second credulous option is provided in Horty [7], which interprets default logic as a deontic logic allowing for moral con icts. 4 Unfortunately, although the treatment of the frame problem suggested here does seem to work for the simple example set out in Section 2.1, it was shown in Hanks and McDermott [6] that this straightforward kind of ....

J. Horty, \Moral Dilemmas and Nonmonotonic Logic" Journal of Philosophical Logic, 23 (1994), 35-65.

....adequate; but as it turns out, this approach cannot be interpreted in any natural way within the framework of modal logic. Section 3 introduces one of the most familiar formalisms for nonmonotonic reasoning, Raymond Reiter s default logic [27] and then reviews a result, first presented in my [16], that justifies an interpretation of van Fraassen s deontic logic into Reiter s default logic. Section 4 explores some technical points concerning van Fraassen s account, and then develops three variant approaches. I believe that these variants approaches, like van Fraassen s original account, ....

....can be used also, it seems, to represent other kinds of norms such as legal or ethical norms and in that case, any relation with probabilistic reasoning will be more distant. It is this reading of defaults as representing norms in general that motivates the connection, first established in [16], between default and deontic logics: if the norms generated by ought statements are represented through default rules, it turns out that van Fraassen s theory of oughts can be interpreted in a straightforward way within Reiter s default logic. Formally, the interpretation is developed as ....

[Article contains additional citation context not shown here]

John Horty. Moral dilemmas and nonmonotonic logic. Journal of Philosophical Logic, 23:35--65, 1994.

....it is studied in the field of Artificial Intelligence and Law, particularly in the work of Ashley [2] and two other fields: deontic logic and nonmonotonic reasoning. The deontic logic appealed to here is a formalism originally inspired by van Fraassen [14] and then developed in more detail in my [7, 9] for reasoning in the presence of conflicting norms. This logic is described in Section 2 of the present paper; although the logic is not new, the presentation has been streamlined considerably. Section 3 shows how to extend this framework to cover the kind of reasoning with conflicting norms ....

....conflicts. From the standpoint of deontic logic, the technical challenge presented by such a view is to design a formalism for reasoning coherently in these situations. This section sketches such a formalism, a deontic logic inspired by van Fraassen [14] and developed in more detail in my [7, 9]. We focus here on a conditional version of this logic, where a conditional ought statement of the form It ought to be that B, given A is symbolized as fl(B=A) Van Fraassen s approach is based on the idea that deontic logic can usefully be formulated against the background of a set of ....

John Horty. Moral dilemmas and nonmonotonic logic. Journal of Philosophical Logic, 23:35--65, 1994.

....that we are given only a linear preference ordering on histories, and seeks to extend this ordering to a partial ordering over sets of histories. This utilities lifting problem is discussed or alluded to, for instance, in [van Fraassen 1972] Jennings 1974] Jennings 1985] Wellman 1988] and [Horty 1994]. But, as far as we can tell, there has never been a systematic attempt to develop a solution to the problem that does justice to the very robust common sense intuitions that people have for assessing judgments of preference over sets of outcomes intuitions that seem in many cases to be largely ....

Horty, J. F. 1994. Moral dilemmas and nonmonotonic logic. Journal of Philosophical Logic 23(1):35--65.

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J. Horty. Moral Dilemmas and Nonmonotonic Logic. In Proc. of the First International Workshop on Deontic Logic in Computer Science, Amsterdam, The Netherlands, 1991.

No context found.

J.F. Horty. Moral dilemmas and nonmonotonic logic. Journal of Philosophical Logic, 23:35-65, 1994.

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J.F. Horty, `Moral dilemmas and nonmonotonic logic', Journal of Philosophical Logic, 23, 35--65, (1994).

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Horty J. Moral dilemmas and nonmonotonic logic. Journal of philosophical logic 1994; 23:35-65.

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J.F. Horty. Moral dilemmas and nonmonotonic logic. Journal of Philosophical Logic, 23:35--65, 1994.

No context found.

J.F. Horty. Moral dilemmas and non-monotonic logic. Journal of Philosophical Logic 23:35--65 (1994).

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