Chisholm’s target in the 1967b paper was a popular collection of views about the metaphysics of modality. Many philosophers — going back perhaps to Leibniz — seem to presuppose these views in their discussions of necessity and possibility. The central doctrine is that there are many possible worlds. The actual world is just one among them, distinguished by the fact that what happens here is what actually happens. To say that a statement is true is just to say that it is true at the actual world. To say that a statement is possible is just to say that it is true at some possible world. To say that a statement is necessary is just to say that it is true at every possible world. Thus we have an account of de dicto modality.