 Suppose that two given logics \({{\cal L}}_1\) and \({{\cal L}}_2\) are to be combined using some technique. It should be obvious that any method applied to combine \({{\cal L}}_1\) and \({{\cal L}}_2\) will create a new logic \({{\cal L}}\) which contains the signature (logic symbols such as connectives, quantifiers, propositional variables etc.) of both logics: \({{\cal L}}\) will be defined in a mixed language, which allows combinations of symbols of the underlying languages. That is, a combination of logic systems presupposes the previous combination of the respective signatures. This is why the choice of the signature of the combined system is as important as the logic itself. For instance, the definition of the language of parameterization is fundamental in order to obtain the intended combined logic (see  subsection 4.5).  Another example is found in Schurz 1991, where the formal treatment of Hume’s ‘is-ought problem’ (recall  section 1)  presupposes careful handling of subtle combinations of languages.