 The fact that algebraic fibring generalizes (at least at the propositional level) the fusion of modal logics makes the former method become very natural and useful. Moreover, the universality of the construction allows one to define algebraic fibring in very different logical contexts (categories of logics), such as non-truth-functional logics, higher-order logics, sequent calculi etc. As it will be shown in  section 5,  the different notions of morphisms between logics affect the strength of the logics obtained by algebraic fibring in the different categories of logic systems. For general accounts of algebraic fibring see, for instance, Caleiro et al. 2005 and Carnielli et al. 2008.