 Despite the above mentioned results on combining heterogeneous logics, it seems more reasonable to combine logics defined in a homogeneous way, and, in fact, this is the case with most of the proposals in the literature. For instance, the usual combinations of modal logics (as fusion, product and fibring) are performed between systems presented axiomatically, or between classes of Kripke models. It is frequent, therefore, to define different categories of logic systems (consequence relations, Hilbert calculi, algebraizable logics etc.) with appropriate morphisms between them, in which the combination (or decomposition) of logics appear as universal constructions. Algebraic fibring, to be described in  subsection 4.3,  is a good example of this approach.