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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.

Terms of service of on-line platforms too often contain clauses that are potentially unfair to the consumer. We present an experimental study where machine learning is employed to automatically detect such potentially unfair clauses. Results show that the proposed system could provide a valuable tool for lawyers and consumers alike.

We propose a computationally oriented non-monotonic multi-modal logic arising from the combination of temporalised agency and temporalised normative positions. We argue about the defeasible nature of these notions and then we show how to represent and reason with them in the setting of Defeasible Logic. MOTIVATION AND LAYOUTAn increasing number of works on agents assume that in artificial societies normative concepts may play a decisive role, allowing for the flexible co-ordination of autonomous agents [5,20,15]. In particular, it seems crucial to model organisations of agents in terms of policy-based normative systems; accordingly an organisation should be characterised by specifying the normative positions relevant to design its structure. These positions include duties, permissions, but also powers, as for instance powers of creating further normative positions on the head of other agents. In this paper we will develop a formal machinery to account for several fundamental concepts that are required to model policy-based normative systems. These concepts will be embedded in a nonmonotonic and computationally-oriented framework based on Defeasible Logic (DL).From the conceptual standpoint, it is well known that the basic deontic qualifications (obligatory, forbidden, permitted and facultative) are not sufficient to capture all fundamental normative notions, such as the concepts of rights and power. For this reason, we will first provide an account in DL of the notion of other-directed obligation [14] to express, e.g., the first Hohfeldian set of fundamental concepts: duty, right, noright, and privilege. Second, we shall focus on different kinds of normative conditionals. This will enable us to characterise also the idea of normative power and articulate many potestative concepts such as the second Hohfeldian set of concepts: power, liability (or, subjection, to avoid confusion with the notion of liability, as used in tort law), disability, and immunity. * This work was partially supported by Australia Research Council under Discovery Project No. DP0558854 on "A Formal Approach to Resource Allocation in Web Service Oriented Composition in Open Marketplaces". Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. In general, we shall see how the analysis of normative conditionality and normative positions has to include temporal aspects in order to capture a number of nuances in the perspective of framing a fine-grained classification of such concepts. In fact, normative determinations take place along the axis of time: Normative preconditions hold or happen in certain temporally characterised occasions, and consequently their effects too hold or happen wi...

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Abstract. In this paper we provide a formal analysis of the idea of normative co-ordination. We argue that this idea is based on the assumption that agents can achieve flexible co-ordination by conferring normative positions to other agents. These positions include duties, permissions, and powers. In particular, we explain the idea of declarative power, which consists in the capacity of the power-holder of creating normative positions, involving other agents, simply by "proclaiming" such positions. In addition, we account also for the concepts of representation, namely the representative's capacity of acting in the name of his principal, and of mandate, which is the mandatee's duty to act as the mandator has requested. Finally, we show how the framework can be applied to represent the contract-net protocol. Some brief remarks on future research and applications conclude this contribution.