Typical human languages (maybe all natural human language) have a "Was" operator that applies to a sentence s and yields a sentence Wast(s) that backdates s to t. Sometimes that operator works by shifting context, but in English it normally works by shifting tense and inserting an "at" (though sometimes a more complex formulation is needed). Thus, perhaps, "Wast(George is talking about Saddam Hussein)" is the sentence: "George was talking about Saddam Hussein at t".
Now, here are two plausible facts about logic and the Wast(s) operator:
- If the proposition that s entails the proposition that u, then the proposition that Wast(s) entails the proposition that Wast(u).
- For every proposition p, p entails the proposition that p is true.
- That Hitler's actions are starting a world war entails that there is or will be a world war.
- Hitler's actions were starting a world war at t. (Historical fact)
- Wast(Hitler's actions are starting a world war). (Paraphrase of 4)
- Wast(There is or will be a world war). (By 1, 3 and 5)
- Wast(The proposition that there is or will be a world war is true). (By 1, 2 and 6)
- The proposition that there is or will be a world war was true on September 1, 1939. (Paraphrase of 7)
Alan Rhoda has already denied (2), calling it "Pruss's mistake". So he won't have any trouble with this argument. But (2) seems rather more plausible than the conjunctions of the premises of the best arguments for open future views.
I should say that I am not sure (2) is true. What I am more sure of is:
- For every proposition p, p entails the material conditional: if p exists, p is true.