ABSTRACT
This table is composed of molecules. Might it not have been composed of molecules? Certainly it was a scientific discovery of great moment that it was composed of molecules (or atoms). But could anything be this very object and not be composed of molecules? Certainly there is some feeling that the answer to that must be “no.” At any rate, it’s hard to imagine under what circumstances you would have this very object and find that it is not composed of molecules. A quite different question is whether it is in fact composed of molecules in the actual world and how we know this. (I will go into more detail about these questions about essence later on.)
I wish at this point to introduce something which I need in the methodology of discussing the theory of names that I’m talking about. We need the notion of “identity across possible worlds” as it’s usually and, as I think, somewhat misleadingly called,1 to explicate one distinction that I want to make now. What’s the difference between asking whether it’s necessary that 9 is greater than 7 or whether it’s necessary that the number of planets is greater than 7? Why does one show anything more about essence than the other? The answer to this might be intuitively “Well, look, the number of planets might have been different from what it in fact is. It doesn’t make any sense, though, to say that nine might have been different from what it in fact is.” Let’s use some terms quasi-technically. Let’s call something a rigid designator if in every possible world it designates the same object, a nonrigid or accidental designator if that is not the case. Of course we don’t require that the objects exist in all possible worlds. Certainly Nixon might not have existed if his parents had not gotten married, in the normal
we usually mean that it is true of that object in any case where it would have existed. A rigid designator of a necessary existent can be called strongly rigid.
