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Argumentation for Normative Reasoning

Journal article published in 2008 by Nir Oren, Michael Luck ORCID, Timothy J. Norman
This paper is available in a repository.
This paper is available in a repository.

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Abstract

An agent's behaviour is governed by multiple factors, including its beliefs/desires/intentions, its reasoning processes and societal influences acting upon it, such as norms. In this paper we propose an extensible argumentation inspired reasoning procedure, and show how it may be used to perform normative reasoning. . The language used by our procedure is built around defeasible, non- monotonic rules called argument schemes. The evaluation of the in- teractions between argument schemes and predicates is performed using a novel argumentation based technique. We show how issues such as normative conflict, priorities over norms, and the effects of norms may be represented using the framework, and how the agent may use these to reason effectively. An increasingly popular way of declaratively controlling agent be- haviour is through the use of norms. Most commonly, a set of obliga- tions and prohibitions are imposed upon an agent, constraining its be- haviour accordingly. Different approaches define these norms in dif- ferent ways. In the simplest case, an obligation can be seen as a hard constraint, with the system entering an undefined state if the norm is violated. More flexible systems treat norms as soft constraints, but as flexibility increases, difficult questions arise in areas including nor- mative reasoning, verification, and semantics, as well as how norms interact with each other. In particular, additional complications arise when normative con- flicts occur, with an agent having to select which norms to honour, and which to ignore. Ultimately, the agent's actions are governed by its preferences, knowledge (including beliefs, desires and intentions), the norms affecting it, and the state of the environment. Several ef- forts to address this issue have been proposed, which take these var- ious factors into account in different ways. One strategy espoused by some (including the philosopher John Pollock (8)) follows the approach that humans appear to use when faced with multiple choices; namely to engage in an internal dia- logue and act based on its outcome. For example, if I am to decide whether to play a game or write a paper, I would weigh up the pros and cons of each of these actions, in the context of my obligations, e.g. when the paper is due, and how much I like my job. This weight- ing process may create additional reasons to pick one action over another, and may cause other reasons to no longer be applicable. Pollock's work was intended to apply to any form of practical rea- soning, and did not pay particular attention to dealing with norms. His internal dialogue based representation of practical reasoning, in- stantiated via an argumentation procedure, is highly appropriate for reasoning about norms because norms typically constrain desired be- haviour, leading to the need to resolve (internal) conflicts so as to allow an agent to determine whether to comply with its norms. Our reasoning framework, while simpler than Pollock's, contains the fea- tures necessary to reason about normative issues. It is based on the emerging AIF standard (3), and provides support for normative con- cepts via the idea of argument schemes. Argument schemes repre- sent defeasible, possibly non-deductive, rules of inference, and are intended to capture common patterns of argument. They may be gen- eral, or domain-specific. In this paper, therefore, we use argument schemes to represent rea- soning rules. We present a number of argument schemes that can be used to reason about normative concepts. By representing its knowl- edge using these argument schemes, and using results from argumen- tation theory, an agent is able to infer, from the interactions between argument schemes, how to act on the basis of its norms, and whether any of its norms should be ignored. Our approach is able to naturally deal with normative conflict and, due to its non-monotonic nature, is easily able to handle cases where an agent is presented with addi- tional information. Apart from the formal introduction of normative argument schemes, our main contribution thus revolves around the framework's ability to aid an agent in resolving normative conflict. Thus, we begin the next section by introducing argument schemes, after which we show how an agent may reason about their interac- tions. After providing an example showing the framework in action, we conclude the paper by examining related research and proposing further extensions to the work presented here.