The aim of this paper is to present a new logic, called LA r s , for the abduction of singular hypotheses. The intended application context of the logic concerns problem solving situations in which one tries to 'abduce' an explanatory hypothesis for an explanandum on the basis of a background theory possibly together with some relevant empirical findings. The intended set of premises will thus typically consist of one or more explananda and some general statements that, with respect to those

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... ticular explananda, are considered as relevant. It may also contain zero or more empirical findings that are relevant (for instance, because they contradict one of the explanantia). The logic presented here is a variant of the logic LA r . 1 Both LA r and LA r s are adaptive logics. Adaptive logics are a family of non-standard logics that are meant to study defeasible reasoning processes in a formally exact way. As will become clear below, the adaptive logics framework is especially suited to formulate formal logics for abduction. 2 The logics LA r and LA r s lead to the same consequence set when applied to the same set of premises. The difference, however, is that LA r s , unlike LA r , is in the so-called "standard format" of adaptive logics. Formulating an adaptive logic in standard format has many advantages. One of them is that both the semantics and the proof theory can be formulated in a * Research for this paper was supported by subventions from Ghent University and from the Research Foundation -Flanders (FWO -Vlaanderen). The author is indebted to the anonymous referees for their helpful suggestions.