Madakkatel, Mohammed Iqbal2013-03-072013-03-072009-0620050062http://bspace.buid.ac.ae/handle/1234/54DISSERTATION WITH DISTINCTIONClassical reasoning such as reasoning based on propositional logic is monotonic in the sense that adding new information does not remove any previously made conclusion. Common sense suggests that the failure of monotonic reasoning is widespread. Many a time, we jump to conclusions and then we correct our conclusions based on further information as it arrives. Reasoning of this kind is called as nonmonotonic reasoning. Recently, the study of nonmonotonic reasoning has appealed to the powerful notion of argument through the proliferation of so-called argumentation systems. A very influential approach to argumentation systems completely abstracts the origin and the internal structure of the arguments. The focus, instead, is on the relationships between these abstract arguments using defeat relations. The defeat structures can be in different forms such as mutual attack (one argument attacks another argument and the attacked argument attacks the attacker), reinstatement (an argument reinstates another argument by defeating the defeater) and a cycle of attack. The obvious question here is to identify which arguments are rejected, accepted and undecided in such defeat structures. Extension-based abstract argument evaluation criteria (also known as extension-based semantics) can be thought of as criteria for making this decision and have been studied in detail in the literature. These evaluation criteria have been mainly developed for obtaining desirable formal or computational properties, largely based on intuition. The cognitive plausibility of such evaluation criteria has mostly been ignored. However, it is crucial to understand the cognitive plausibility of such evaluation criteria if we are to build software agents capable of interacting persuasively with humans through arguments. This study is an attempt to explore the cognitive plausibility of abstract argument evaluation criteria. Cognitive plausibility of abstract argument evaluation criteria is explored by conducting psychological experiments. Scenarios of standard reinstatement (an argument reinstating another argument by defeating the defeater) and the floating reinstatement (two mutually conflicting arguments reinstating another argument by defeating the defeater) are studied in detail. The empirical results show that the notion of reinstatement in abstract argumentation is cognitively plausible by supporting both grounded and preferred semantics. The results also show that the notion of floating reinstatement is cognitively plausible by not supporting the grounded semantics. Lack of a significant interaction between the pattern and the reasoners' preference (or lack of preference) for one of the two mutually conflicting defenders in the tests indicates the existence of a different cognitively plausible notion that cannot be explained using the abstract argument evaluation criteria. The notion is that there is no clear endorsement for both credulous preferred and sceptical preferred semantics in floating reinstatement. The results also suggest that a floating reinstatement has an e ect that is not signi cantly different from that of the standard form. That is, the mutually conflicting nature of defenders does not play any role that undermines the job of reinstating the main argument. Importantly, only partial recovery is achieved in both scenarios of reinstatement and the idea of such a partial recovery is not dealt with in the abstract argumentation theory.encognitive plausibilitymonotonicabstract argumentDissertation