Assessing relevance

This paper advances an approach to relevance grounded on patterns of material inference called argumentation schemes, which can account for the reconstruction and the evaluation of relevance relations. In order to account for relevance in different types of dialogical contexts, pursuing also non-cognitive goals, and measuring the scalar strength of relevance, communicative acts are conceived as dialogue moves, whose coherence with the previous ones or the context is represented as the conclusion of steps of material inferences. Such inferences are described using argumentation schemes and are evaluated by considering 1) their defeasibility, and 2) the acceptability of the implicit premises on which they are based. The assessment of both the relevance of an utterance and the strength thereof depends on the evaluation of three interrelated factors: 1) number of inferential steps required; 2) the types of argumentation schemes involved; and 3) the implicit premises required

Computing Strong and Weak Permissions in Defeasible Logic

In this paper we propose an extension of Defeasible Logic to represent and compute three concepts of defeasible permission. In particular, we discuss different types of explicit permissive norms that work as exceptions to opposite obligations. Moreover, we show how strong permissions can be represented both with, and without introducing a new consequence relation for inferring conclusions from explicit permissive norms. Finally, we illustrate how a preference operator applicable to contrary-to-duty obligations can be combined with a new operator representing ordered sequences of strong permissions which derogate from prohibitions. The logical system is studied from a computational standpoint and is shown to have liner computational complexity

Defeasibility and Balancing

“Defeasibility” and “balancing” are expressions introduced in recent times to deal with long-standing legal phenomena, which in the context of the constitutional state acquire a special prominence. What is at issue, in fact, is the necessity to recognise exceptions implicit in the norms, in order to provide the legal system with the flexibility needed to maximise the chances of finding a correct—just—answer without abandoning the legal system; and (which to a large extent is another aspect of the same phenomenon) to resolve difficult cases (those for which there is no predefined rule, but only principles) argumentatively, by resorting to a procedure, balancing, the use of which does not necessarily imply an exercise in arbitrariness, although it does involve certain risks that recommend a prudent and limited use of this resource. The last part of the paper summarises the ideas that legal theorists and practitioners should bear in mind in order to understand and make proper use of these two controversial but indispensable notions

Defeaters as Indicators of Ignorance

In this paper, we propose a new theory of rationality defeat. We propose that defeaters are indicators of ignorance, evidence that we’re not in a position to know some target proposition. When the evidence that we’re not in a position to know is sufficiently strong and the probability that we can know is too low, it is not rational to believe. We think that this account retains all the virtues of the more familiar approaches that characterise defeat in terms of its connection to reasons to believe or to confirmation but provides a better approach to higher-order defeat. We also think that a strength of this proposal is that it can be embedded into a larger normative framework. On our account the no-defeater condition is redundant. We can extract our theory of defeat from our theory of what makes it rational to believe—it is rational to believe when it is sufficiently probable that our belief would be knowledge. Thus, our view can provide a monistic account of defeat, one that gives a unifying explanation of the toxicity of different defeaters that is grounded in a framework that either recognises knowledge as the norm of belief or identifies knowledge as the fundamental epistemic good that full belief can realise

Defeasibility and Practical Errors

Defeasibility is usually understood as the possibility that rules contain implicit exceptions. It is a problem that has generated a wide bibliography in the last decades, normally linked to analytic legal positivism. The present paper will deal with the matter of defeasibility as a theoretical problem, that is, a problem of the theories of law. In particular, two of the most refined proposals of contemporary legal positivism will be analyzed: the deep conventionalism of Juan Carlos Bayón and the inclusive legal positivism of José Juan Moreso and his theory of defeaters. Once these positions have been analyzed, the basic theses of legal postpositivism will be presented, highlighting the idea of practical error, showing how for legal postpositivism the problem of defeasibility is nothing other than that of the rationality of legal decisions, of making implicit law explicit, and that in this regard there are rational criteria that help us to solve hard cases and avoid making practical errors