 The sensitivity to logical framework of issues of unique characterization is well illustrated with the case of modal logic. It is possible to fabricate special purpose logical frameworks which allow for the formulation of rules uniquely characterizing ☐ in all normal modal logics (Blamey and Humberstone 1991), but without such exotic devices, unique characterization is limited to the case in which ☐ is fully determined—among the normal modal logics, then, just to that for which ⊢ ☐φ for all φ, and that in which φ ⊣⊢ ☐φ for all φ.  (Note  34 is relevant here. The “⊢” just used stands for the local consequence relation concerned so we could equally well have written, “⊢ φ ↔ ☐ φ”. Even more exotic logical frameworks for modal logic – taking us further still from the idea of an argument with premisses and conclusion(s), that is – have been proposed than that just alluded to, several of which are described in Poggiolesi and Restall 2012 and in the literature cited in their bibliography.)