THE VALUE OF THE 4 VALUES

In his well-known paper ''How computer should think'' Belnap (1977) ar gues that four-valued semantics is a very suitable setting for compute rized reasoning. In this paper we vindicate this thesis by showing tha t the logical role that the four-valued structure has among Ginsberg's bilattices is similar to the role that the two-valued algebra has amo ng Boolean algebras. Specifically, we provide several theorems that sh ow that the most useful bilattice-valued logics can actually be charac terized as four-valued inference relations. In addition, we compare th e use of three-valued logics with the use of four-valued logics, and s how that at least for the task of handling inconsistent or uncertain i nformation, the comparison is in favor of the latter. (C) 1998 Elsevie r Science B.V. All rights reserved.