 In order to use systems with multiple modalities, the question is how to build such settings. One of the most important points is to decide whether one of the concepts to be studied is ‘more fundamental’ than the other, in the sense that the latter can be defined in terms of the former. As mentioned, the famous understanding of knowledge as justified true belief is one of the most notable examples. Others are equally relevant, as a definition of beliefs in terms of the available arguments/evidence/justifications, or a definition of epistemic notions for a group in terms of the epistemic notions of its members. Yet, the basic alethic modal logic of necessity and possibility already provides a paradigmatic example of how to define the relationship between two concepts.