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University of Otago

1. Aucher, Guillaume. Perspectives on belief and change .

Degree: 2008, University of Otago

This thesis is about logical models of belief (and knowledge) representation and belief change. This means that we propose logical systems which are intended to represent how agents perceive a situation and reason about it, and how they update their beliefs about this situation when events occur. These agents can be machines, robots, human beings. . . but they are assumed to be somehow autonomous. The way a fixed situation is perceived by agents can be represented by statements about the agents' beliefs: for example 'agent A believes that the door of the room is open' or 'agent A believes that her colleague is busy this afternoon'. 'Logical systems' means that agents can reason about the situation and their beliefs about it: if agent A believes that her colleague is busy this afternoon then agent A infers that he will not visit her this afternoon. We moreover often assume that our situations involve several agents which interact between each other. So these agents have beliefs about the situation (such as 'the door is open') but also about the other agents' beliefs: for example agent A might believe that agent B believes that the door is open. These kinds of beliefs are called higher-order beliefs. Epistemic logic [Hintikka, 1962; Fagin et al., 1995; Meyer and van der Hoek, 1995], the logic of belief and knowledge, can capture all these phenomena and will be our main starting point to model such fixed ('static') situations. Uncertainty can of course be expressed by beliefs and knowledge: for example agent A being uncertain whether her colleague is busy this afternoon can be expressed by 'agent A does not know whether her colleague is busy this afternoon'. But we sometimes need to enrich and refine the representation of uncertainty: for example, even if agent A does not know whether her colleague is busy this afternoon, she might consider it more probable that he is actually busy. So other logics have been developed to deal more adequately with the representation of uncertainty, such as probabilistic logic, fuzzy logic or possibilistic logic, and we will refer to some of them in this thesis (see [Halpern, 2003] for a survey on reasoning about uncertainty). But things become more complex when we introduce events and change in the picture. Issues arise even if we assume that there is a single agent. Indeed, if the incoming information conveyed by the event is coherent with the agent's beliefs then the agent can just add it to her beliefs. But if the incoming information contradicts the agent's beliefs then the agent has somehow to revise her beliefs, and as it turns out there is no obvious way to decide what should be her resulting beliefs. Solving this problem was the goal of the logic-based belief revision theory developed by Alchourrón, Gärdenfors and Makinson (to which we will refer by the term AGM) [Alchourrón et al., 1985; Gärdenfors, 1988; Gärdenfors and Rott, 1995]. Their idea is to introduce 'rationality postulates' that specify which belief revision operations can be considered as being 'rational'… Advisors/Committee Members: van Ditmarsch, Hans (advisor).

Subjects/Keywords: knowledge representation (Information theory); artificial intelligence; social aspects; expert systems (Computer science)

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APA (6th Edition):

Aucher, G. (2008). Perspectives on belief and change . (Doctoral Dissertation). University of Otago. Retrieved from

Chicago Manual of Style (16th Edition):

Aucher, Guillaume. “Perspectives on belief and change .” 2008. Doctoral Dissertation, University of Otago. Accessed July 14, 2020.

MLA Handbook (7th Edition):

Aucher, Guillaume. “Perspectives on belief and change .” 2008. Web. 14 Jul 2020.


Aucher G. Perspectives on belief and change . [Internet] [Doctoral dissertation]. University of Otago; 2008. [cited 2020 Jul 14]. Available from:

Council of Science Editors:

Aucher G. Perspectives on belief and change . [Doctoral Dissertation]. University of Otago; 2008. Available from: