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0 pointszozbot2349mo ago0 comments

> emphatically DOES NOT demonstrate the constructive existence of such an oracle

Of course, but it shows that you can assume that such an oracle exists whenever you are working under additional conditions where the existence of such a "special case" oracle makes sense to you, even though you can't show its existence in the general case. This outlook generalizes to all non-constructive existence statements (and disjunctive statements, as appropriate). It's emphatically not the same as constructive existence, but it can nonetheless be useful.

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btilly9mo ago· 2 in thread

That's like asserting the existence of a bank account in my name with a billion dollars in it that I know nothing about.

I won't ever be able to find a contradiction from that claim, because I have no way to find that bank account if it exists.

But that argument also won't convince me that the bank account exists.

zozbot234OP9mo ago

That argument ought to convince you that there's a mere "possible world" where that bank account turns out to exist. Sometimes we are implicitly interested in these special-cased "possible worlds", even though they'll involve conditions that we aren't quite sure about. Non-constructive existence is nothing more than a handy way of talking about such things, compared to the constructively correct "it's not the case that the existence of X is always falsified".

btilly9mo ago

It would be weird for a constructivist to be interested in a possible world that they don't believe exists.

Theoretically possible? Sure. But the kinds of questions that lead you there are generally in opposition to the kinds of principles that lead someone to prefer constructivism.

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