I'm wondering if we should have a tag for the set theory NFU. On the one hand, I personally would like to see the tag stick around, since I think NFU is a very interesting and potentially useful set theory. On the other hand, as far as I can tell, only three questions have ever been asked about NFU (counting one I asked today).

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    $\begingroup$ I've added a link to the New Foundations Wikipedia site. You might want to add some description to this question of exactly what NFU is. $\endgroup$
    – robjohn Mod
    Commented Oct 7, 2012 at 16:48
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    $\begingroup$ I noticed earlier that the other two nfu questions were recently edited, with the only change the addition of the nfu tag. I just noticed that you were the one making these edits. Upon further inspection, it seems that the nfu tag was created at about the same time as the aforementioned edits. Did you happen to create this tag? $\endgroup$
    – user642796
    Commented Oct 7, 2012 at 17:32
  • $\begingroup$ @Arthur Yes, I did. $\endgroup$ Commented Oct 7, 2012 at 23:36
  • $\begingroup$ I will add link to a recent question about related (but broader) tag: Tag for alternative set theories?. $\endgroup$ Commented Apr 22, 2018 at 16:48

2 Answers 2


I don't think three questions is worth having a tag for. I even doubt a new-foundations tag would be viable.

If we are to do something in this area. I would prefer to have an axiomatic-set-theory which wouldn't be as likely to attract elementary questions from askers who don't really care about axiom systems as the current set-theory. (They are supposed to go in elementary-set-theory, even relatively advanced ones about ordinals -- but elementary-foo tags are a blight in general; they are hard to discover for the users who need them most).

Tags are fairly cheap, but not free -- at a minimum unused tags have the downside of showing up when the system suggests tags for new question, creating confusion for new users who have to guess at which tags are actually appropriate for their new questions.

  • $\begingroup$ Yes, I like this solution. (Should I accept it? I feel like it's not my place to say that it's the correct solution.) Should we rename nfu to axiomatic-set-theory, then? $\endgroup$ Commented Oct 7, 2012 at 23:40
  • $\begingroup$ I think "nfu" is fine, it may be even better to call it "new-foundations", though it brings a slight risk of wrongly tagged questions. But "axiomatic-set-theory" is definitely the wrong tag (By default, this refers to ZFC, its fragments, variants, and extensions). $\endgroup$ Commented Oct 8, 2012 at 16:03
  • $\begingroup$ I'm curious how you see these three set-theory tags interacting. I have a feeling that set-theory and axiomatic-set-theory would have a negligible symmetric difference. $\endgroup$
    – user642796
    Commented Oct 8, 2012 at 16:55
  • $\begingroup$ @ArthurFischer: There would still only be two tags. I'm imagining moving the current "set-theory" to "axiomatic-set-theory" and then perhaps "elementary-set-theory" to "set-theory". $\endgroup$ Commented Oct 8, 2012 at 16:58
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    $\begingroup$ I would actually leave the tags as set-theory and elementary-set-theory, if this is the road we are heading. Some questions on "axiomatic-..." would be elementary, some would be advanced, and the useful distinction we currently have would be lost. $\endgroup$ Commented Oct 8, 2012 at 18:02

I don't have a problem with the (brand-new) nfu tag, per se, but my preference would be a catch-all (or at least catch-a-little-bit-more) new-foundations tag. This would add perhaps two or three questions to the tag.


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