Base Belief Change for Finitary Monotonic Logics Pere Pardo 1 , Pilar Dellunde 1,2 , and Llu´ ıs Godo 1 1 Institut d’Investigaci´o en Intel·lig` encia Artificial (IIIA - CSIC) 08193 Bellaterra, Spain 2 Universitat Aut`onoma de Barcelona (UAB) 08193 Bellaterra, Spain Abstract. We slightly improve on characterization results already in the literature for base revision. We show that consistency-based partial meet revision operators can be axiomatized for any sentential logic S satisfying finitarity and monotonicity conditions (neither the deduction theorem nor supraclassicality are required to hold in S ). A characteri- zation of limiting cases of revision operators, full meet and maxichoice, is also offered. In the second part of the paper, as a particular case, we focus on the class of graded fuzzy logics and distinguish two types of bases, naturally arising in that context, exhibiting different behavior. Introduction This paper is about (multiple) base belief change, in particular our results are mainly about base revision, which is characterized for a broad class of logics. The original framework of Alchourr´ on, G¨ ardenfors and Makinson (AGM) [1] deals with belief change operators on deductively closed theories. This framework was generalized by Hansson [9, 10] to deal with bases, i.e. arbitrary set of formulas, the original requirement of logical closure being dropped. Hansson characterized revision and contraction operators in, essentially, monotonic compact logics with the deduction theorem property. These results were improved in [11] by Hansson and Wassermann: while for contraction ([11, Theorem 3.8]) it is shown that finitarity and monotony of the underlying logic suffice, for revision (Theorem [11, Theorem 3.17]) their proof depends on a further condition, Non-contravention : for all sentences ϕ, if ¬ϕ ∈ Cn S (T ∪{ϕ}), then ¬ϕ ∈ Cn S (T ). In this paper we provide a further improvement of Hansson and Wasser- mann’s results by proving a characterization theorem for base revision in any finitary monotonic logic. Namely, in the context of partial meet base revision, we show that Non-contravention can be dropped in the characterization of revision if we replace the notion of unprovability (remainders) by consistency in the defi- nition of partial meet, taking inspiration from [4]. This is the main contribution of the paper, together with its extension to the characterization of the revision operators corresponding to limiting cases of selection functions, i.e. full meet and maxichoice revision operators.