Are all concrete objects contingent objects and all abstract objects noncontingent objects? Thank you!

I'm inclined to say that all concrete objects are contingent. But those who believe that God exists noncontingently would likely disagree, because according to standard versions of theism God is a concrete object, since God has causal power.

But I'm inclined to say that not all contingent objects are concrete. The Eiffel Tower is a concrete object, whereas the set whose only member is the Eiffel Tower -- the set {The Eiffel Tower} -- is an abstract object, as all sets are. The identity of any set depends solely on its membership: had any member of a given set failed to exist, then the set itself would have failed to exist. Therefore, because the Eiffel Tower exists only contingently, the non-empty set {The Eiffel Tower} itself exists only contingently. Indeed, any set containing at least one contingent member is itself a contingent, abstract object. Or so it seems to me.

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