Does Necessity Mandate Uniqueness?

Question

Suppose there is a nonzero number of contingent entities and a nonzero number of necessary entities. For example, the law of non-contradiction is probably a plausible candidate for something that exists in all possible worlds. But surely there are many other such candidates.

But I have seen the claim (this being perhaps the clearest form I've seen the claim take) that any two existing entities are partially contingent upon each other so as to be non-identical/not-the-same-entity/two-entities (i.e. the differentness and separateness of the two is contingent upon each other), thus making them . . . well, contingent instead of necessary. (I have seen similar statements that a necessary entity needs to be monolithic, since otherwise it would be contingent upon its components.)

Is this claim accurate, or is it a fallacy of some sort? Can a single world (possible or actual) contain more than one necessary entity, or can only impossible worlds do that?

Answer 1

If necessity is glossed in terms of David Lewis' counterpart theory as spanning all possible worlds, then there is some loss of uniqueness involved; perhaps each counterpart is special per its world, but the necessary being that they constitute is then "contingent upon" those counterparts existing and spanning all possible worlds, and the "is a counterpart of" relation seems rather far from being uniquely satisfied by the counterparts.

A similar, or even stronger, "problem" for uniqueness might arise if we went with non-Lewisian transworld identity. Suppose transworld identity is akin to identity under a universal, i.e. each surrogate for the counterpart relation in each non-Lewisian possible world is a repetition of a transworld individual universal(!). An absolutely necessary being in the sense of existing in all possible worlds, then, seems to be repeated entirely in every world, which sounds like it goes against pictures of uniqueness.

Answer 2

A proposition is defined to be contingent if it holds in at least one possible word but does not hold in all possible worlds. Accordingly

• an event is contingent if it happens in at least one possible word but does not happen in all possible worlds.
• an entity is contingent if it exist in at least one possible word but does exist in all possible worlds.

If one considers two different entities then they may exist independently of each other – e.g., removing one does not change the other – or they may be dependent on each other. But that’s different from the question whether each separate entity exists contingently or not.

In addition, if two entities exists necessarily as a pair, then one can aks, whether it is more helpful for an ontological consideration to focus on the pair: Does the pair exist contingently or not?

Answer 3

Does Necessity Mandate Uniqueness?

Who knows?

For sure we can say(?): Non-necessity does not mandate Non-Uniqueness..?

And when you mean by "Uniqueness" some sort of "identification" (as of the "needed entities", as of the "necessing individual or group"), then I would tend to give you absolutely right:

Yes, Necessity mandates Uniqueness/identification.