Modelling uncertain positive and negative reasons in decision aiding

The use of positive and negative reasons in inference and decision aiding is a recurrent issue of investigation as far as the type of formal language to use within a DSS is concerned. A language enabling to explicitly take into account such reasons is Belnap's logic and the four valued logics derived from it. In this paper, we explore the interpretation of a continuous extension of a four valued logic as a necessity degree (in possibility theory). It turns out that, in order to take full advantage of the four values, we have to consider “sub-normalised” necessity measures. Under such a hypothesis four valued logics become the natural logical frame for such an approach.