 we can now have world duplicates. What is most important about the detachment of the elements of \(K\) from the evaluation function is that it opens the door to the general consideration of modal frames, sets of worlds plus a binary relation between them, and the correspondence of such frames to modal systems. So, the second new element of the paper, the introduction of a relation \(R\) between the elements of \(K\), naturally accompanies the first. Let it be emphasized once again that the idea of a relation between worlds is not new to Kripke. For example, it is already present as an alternativeness relation in Montague 1960, Hintikka 1961, and Prior 1962, where the idea is attributed to Peter Geach.