This question was deleted by a moderator (which prevents voting to undelete, hence we have to talk about it here instead). The question is all about logic, which is listed in the help center as a valid topic for questions.

In the past, we have had problems with people posting "logic questions" that are little more than "help me prove X in system Y." This question was not of that form.

The close reason given was the "not about philosophy" reason, but I'm not sure that this rationale can be applied to this question. Logic is a branch of philosophy, and this is a question about logic. Yes, it also relates to mathematics, but only insofar as logic relates to math. It is not asking for a detailed mathematical writeup of ZFC, nor for a proof of some specific mathematical theorem, but for a high-level overview of how ZFC manages to accomplish some things that superficially look like they can only be done in second order logic. In other words, the questioner observed that mathematicians have managed to contort one variety of logic into emulating some reasonably large subset of another logic, and asked how they did that. That is a question of interest to both mathematicians and philosophers, and should not be rejected on that basis.

In writing this Meta question, I have attempted to guess what the close votes were all about. This is the problem with "not about philosophy" - it turns every closure into a guessing game where I have to try and read the close voters' minds. There were no comments on the question explicitly suggesting that close voters were objecting to its mathematical aspects - and for all I know, they had some entirely unrelated objection and I've just wasted my time writing the above paragraphs. I'm tempted to propose we abolish the close reason entirely, but I have seen valid uses of it in the past.

Regardless of the fate of that close reason, I strongly believe this question should not have been deleted, and probably should not have been closed.

1 Answer 1


While I had nothing to do with the actions, I am also a bit torn on that.

The problem here is that materially, yes, this is an on-topic question.

Yet, it is a question that

  1. Comes down to "what is the difference between first-order and second-order arithmetic?", a question that has been asked and answered several times on this site already.
  2. Does present this in a way that is frequent with this user: throwing catchy terms around and constructing seemingly interesting challenges to common knowledge whereby the real expert will see in seconds that there is an obvious lack in understanding the concepts used in the first place.

Since especially the latter is a common problem with many questions of this user (sometimes more, sometimes less obvious), I guess people are just fed up with this style of asking that, in a sense, does waste everyone's resources by posting long-winded exposés using terms that are not well understood by the author, while putting in the work to try to understand (or ask for explanations of) these terms would have saved everyone a lot of energy and be more useful for the site.

That may sound harsh but that's a reflection of what I gained as an impression from comments and reactions on these questions by people unlike me (ie. actually knowledgeable in logic and maths).

  • Respectfully, I disagree with this answer. You cite valid reasons to downvote, but I do not believe they are valid reasons to delete the question. If the question is a duplicate of another question, it could be closed as such, but deletion of duplicates is actively discouraged because duplicates serve as signposts to help future searchers find relevant answers. The other thing I find frustrating here, is the fact that the issue you describe appears nowhere in the question's comments, so from my perspective, it looks like an on-topic question was closed "out of the blue."
    – Kevin
    Commented Apr 19 at 21:04

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