An abstract framework for structured arguments is presented, which instantiates Dung's ('On the Acceptability of Arguments and its Fundamental Role in Nonmonotonic Reasoning, Logic Programming, and n- Person Games', Artificial Intelligence , 77, 321-357) abstract argumentation frameworks. Arguments are defined as inference trees formed by applying two kinds of inference rules: strict and defeasible rules. This naturally leads to three ways of attacking an argument: attacking a premise, attacking a conclusion and attacking an inference. To resolve such attacks, preferences may (...) be used, which leads to three corresponding kinds of defeat: undermining, rebutting and undercutting defeats. The nature of the inference rules, the structure of the logical language on which they operate and the origin of the preferences are, apart from some basic assumptions, left unspecified. The resulting framework integrates work of Pollock, Vreeswijk and others on the structure of arguments and the nature of defeat and extends it in several respects. Various rationality postulates are proved to be satisfied by the framework, and several existing approaches are proved to be a special case of the framework, including assumption-based argumentation and DefLog. (shrink)

Inspired by legal reasoning, this paper presents a formal framework for assessing conflicting arguments. Its use is illustrated with applications to realistic legal examples, and the potential for implementation is discussed. The framework has the form of a logical system for defeasible argumentation. Its language, which is of a logic-programming-like nature, has both weak and explicit negation, and conflicts between arguments are decided with the help of priorities on the rules. An important feature of the system is that these priorities (...) are not fixed, but are themselves defeasibly derived as conclusions within the system. Thus debates on the choice between conflicting arguments can also be modelled.The proof theory of the system is stated in dialectical style, where a proof takes the form of a dialogue between a proponent and an opponent of an argument. An argument is shown to be justified if the proponent can make the opponent run out of moves in whatever way the opponent attacks. Despite this dialectical form, the system reflects a declarative, or relational approach to modelling legal argument. A basic assumption of this paper is that this approach complements two other lines of research in AI and Law, investigations of precedent-based reasoning and the development of procedural, or dialectical models of legal argument. (shrink)

The representation and classification of the structure of natural arguments has been one of the most important aspects of Aristotelian and medieval dialectical and rhetorical theories. This traditional approach is represented nowadays in models of argumentation schemes. The purpose of this article is to show how arguments are characterized by a complex combination of two levels of abstraction, namely, semantic relations and types of reasoning, and to provide an effective and comprehensive classification system for this matrix of semantic and quasilogical (...) connections. To this purpose, we propose a dichotomous criterion of classification, transcending both levels of abstraction and representing not what an argument is but how it is understood and interpreted. The schemes are grouped according to an end-means criterion, which is strictly bound to the ontological structure of the conclusion and the premises. On this view, a scheme can be selected according to the intended or reconstructed purpose of an argument and the possible strategies that can be used to achieve it. (shrink)

It has long ben recognised that there are referential uses of definite descriptions. It is not as widely recognised that there are atttributives uses of idexicals and other such paradigmatically singular terms. I offer an account of the referential/attributive distinction which is intended to give a unified treatment of both sorts of cases. I argue that the best way to account for the referential/attributive distinction is to treat is as semantically underdetermined which sort of propositions is expressed in a context. (...) In certain contexts the proposition expressed will be a descriptive one, and in others it will be an object-dependent one. I appeal to Sperer and Wilson's (1986) idea that the recovery of the content of an utterance involves pragmatic processes of enrichment of a representation of the logical form of utterance. According to the account I offer, the first-level descriptive meaning associated with an expression (whether this is an indexical or a definite description) is pragmatically enriched and then used either to track an individual in the context, or is taken to lay down a condition of satisfaction for an individual. The proposition that the listener takes the speaker to have expressed is recovered on the basis of considerations of relevance and contextually available information about the speaker's directive intentions. Although my account has affinities with those of Recanati (1993) and Nunberg (1993), it also differs from theirs in crucial ways. Each of these authors sees asymmetries where I see none. I give reasons for preferring my symmetrical account. (shrink)

One of the crucial problems of argumentation schemes as illustrated in (Walton, Reed & Macagno 2008) is their practical use for the purpose of analyzing texts and producing arguments. The high number and the lack of a classification criterion make this instrument extremely difficult to apply practically. The purpose of this paper is to analyze the structure of argumentation schemes and outline a possible criterion of classification based on alternative and mutually-exclusive possibilities. Such a criterion is based not on what (...) an argument is, but how it can be understood and interpreted. The schemes are grouped according to an end-means principle, which is strictly bound to the ontological structure of the conclusion and the premises. On this view, a scheme can be selected according to the intended or reconstructed purpose of an argument and the possible strategies that can be used to achieve it. (shrink)

The problem of establishing the best interpretation of a speech act is of fundamental importance in argumentation and communication in general. A party in a dialogue can interpret another’s or his own speech acts in the most convenient ways to achieve his dialogical goals. In defamation law this phenomenon becomes particularly important, as the dialogical effects of a communicative move may result in legal consequences. The purpose of this paper is to combine the instruments provided by argumentation theory with the (...) advances in pragmatics in order to propose an argumentative approach to meaning reconstruction. This theoretical proposal will be applied to and tested against defamation cases at common law. Interpretation is represented as based on a hierarchy of interpretative presumptions. On this view, the development of the logical form of an utterance is regarded as the result of an abductive pattern of reasoning in which various types of presumptions are confronted and the weakest ones are excluded. Conflicts of interpretations and equivocation become essentially interwoven with the dialectical problem of fulfilling the burden of defeating a presumption. The interpreter has a burden of explaining why a given presumption is subject to default, assuming that the speaker is reasonable and acting based on a set of shared expectations. (shrink)

Reasoning from negative evidence takes place where an expected outcome is tested for, and when it is not found, a conclusion is drawn based on the significance of the failure to find it. By using Gricean maxims and implicatures, we show how a set of alternatives, which we call a paradigm, provides the deep inferential structure on which reasoning from lack of evidence is based. We show that the strength of reasoning from negative evidence depends on how the arguer defines (...) his conclusion and what he considers to be in the paradigm of negated alternatives. If we negate only two of the several possible alternatives, even if they are the most probable, the conclusion will be weak. However, if we deny all possible alternatives, the reasoning will be strong, and even in some cases deductively valid. (shrink)

In this paper, it is shown (1) that there are two schemes for argument from analogy that seem to be competitors but are not, (2) how one of them is based on a distinctive type of similarity premise, (3) how to analyze the notion of similarity using story schemes illustrated by some cases, (4) how arguments from precedent are based on arguments from analogy, and in many instances arguments from classification, and (5) that when similarity is defined by means of (...) episode schemes, we can get a clearer idea of how it integrates with the use of argument from classification and argument from precedent in case-based reasoning by using a dialogue structure. (shrink)

This paper describes a model of legal reasoning and a logic for reasoning with rules, principles and goals that is especially suited to this model of legal reasoning. The paper consists of three parts. The first part describes a model of legal reasoning based on a two-layered view of the law. The first layer consists of principles and goals that express fundamental ideas of a legal system. The second layer contains legal rules which in a sense summarise the outcome of (...) the interaction of the principles and goals for a number of case types. Both principles, goals and rules can be used in legal arguments, but their logical roles are different. One characteristic of the model of legal reasoning described in the first part of the paper is that it takes these logical differences into account. Another characteristic is that it pays serious attention to the phenomena of reasoning about the validity and acceptance of rules, respectively principles and goals, and about the application of legal rules, and the implications of these arguments for the use of rules, principles and goals in deriving legal conclusions for concrete cases.The second part of the paper first describes a logic (Reason-Based Logic) that is especially suited to deal with legal arguments as described in terms of the previously discussed model. The facilities of the logic are illustrated by means of examples that correspond to the several aspects of the model. (shrink)

A judicious collection of old and new, these volumes include sixteen essays published in the 1980s and 1990s, nine published since 2000, and six new essays.

Juristic argumentation must in normal cases lead to a positive conclusion. The adoption of the rules of the burden of argumentation is, therefore, necessary. It is the task of the normative theory of juristic argumentation to formulate and to justify these rules., The rules of the burden of argumentation are constitutive rules. They do not impose duties or obligations to justify, but they state under what conditions a thesis counts as justified. The basic problem lies in the second‐order justification, that (...) is, in the justification of the rules of the burden of argumentation. Their rational justification is a precondition for rational juristic discourse. (shrink)