Combining logics has become a rapidly expanding enterprise that is inspired mainly by concerns about modularity and the wish to join together tailored made logical tools into more powerful but still manageable ones. A natural question is whether it offers anything new over and above existing standard languages. By analysing a number of applications where combined logics arise, we argue that combined logics are a potentially valuable tool in applied logic, and that endorsements of standard languages often miss the point. Using the history of quantified modal logic as our main example, we also show that the use of combined structures and logics is a recurring theme in the analysis of existing logical systems.

General (acm F.4.0), Mathematical Logic (acm F.4.1), Knowledge Representation Formalisms and Methods (acm I.2.4)
Theory of mathematical modeling (msc 00A71), Modal logic (including the logic of norms) (msc 03B45)
CWI
Department of Computer Science [CS]

Blackburn, P, & de Rijke, M. (1995). Why combine logics?. Department of Computer Science [CS]. CWI.