## DefLog: on the logical interpretation of prima facie justified assumptions## Bart Verheij## AbstractAssumptions are often not considered to be definitely true, but only as prima facie justified. When an assumption is prima facie justified, there can for instance be a reason against it, by which the assumption is not actually justified. The assumption is then said to be defeated. This requires a revision of the standard conception of logical interpretation of sets of assumptions in terms of their models. Whereas in the models of a set of assumptions, all assumptions are taken to be true, an interpretation of prima facie justified assumptions must distinguish between the assumptions that are actually justified in the interpretation and those that are defeated.In the present paper, the logical interpretation of prima facie justified assumptions is investigated. The central notion is that of a dialectical interpretation of a set of
assumptions. The basic idea is that a prima facie justified assumption is
not actually justified, but defeated when its so-called dialectical
negation is justified. The properties of dialectical
interpretation are analyzed by considering partial dialectical
interpretations, or stages, and by establishing the notion of
dialectical justification. The latter leads to a characterization
of the existence and multiplicity of the dialectical interpretations of a
set of assumptions. Since dialectical interpretations are a variant of
stable semantics, the results are relevant for existing work on nonmonotonic
logic and defeasible reasoning, on which the present work builds. Instead of focusing on defeasible rules or arguments, the present approach is sentence-based. A particular innovation is the use of a conditional that is prima facie justified (just like other assumptions) instead of an inconclusive conditional. Publisher's page Manuscript Reference:
Verheij, Bart (2003). DefLog: on the logical interpretation of prima facie justified assumptions. Journal of Logic and Computation,
Vol. 13, No. 3, pp. 319-346. For a lot of additional material, see the technical report 'DefLog - a logic of dialectical justification and defeat'. Bart Verheij's home page - research - publications |