Under what circumstances should a question be made community wiki?

Probably any question asking for a list of something (e.g. 1) must be CW. What else? What about questions asking for a list of applications of something (like, say, 3) or questions like 2? Should all soft-questions be made community wiki (and how we should define soft-question, in that case)?

  • $\begingroup$ related: tea.mathoverflow.net/discussion/6/… $\endgroup$
    – Grigory M
    Commented Aug 4, 2010 at 6:51
  • 3
    $\begingroup$ 1 is asking for an extremely broad list and is not a direct maths question. That makes it a clear CW. Questions 2 and 3 are less broad and more maths related, so their status is less clear. I think that if someone asked about interesting properties of a circle though that everyone would agree that it should be a CW $\endgroup$
    – Casebash
    Commented Aug 4, 2010 at 7:12

5 Answers 5


Due to the nature of community wiki, this is quite a difficult question to answer. I think that we should be conservative in our enforcement of CW, so that when we do enforce it, there is a general consensus. Without consensus CW will cause unnecessary confusion and turn users off our site.

I think it is good to review how CW seems to have come about. StackOverflow (the original StackExchange site) is not designed for discussions. The rearranging of answers and the limitations on comments make it a poor tool for this. These limitation aren't just due to technical reasons - our founders had noticed that forums seems to be dominated by never-ending discussion on "What is the best programming language?" or "What is the best university?". This is why questions without a real answer are discouraged.

However, it soon became apparent that there are a class of question without a definite answer - poll questions - where StackOverflow works reasonably well. While new answers to old questions get buried at the end, the top few answers tend to be really good. These question had to be allowed because they enjoy such a large amount of community support (with a small, but very vocal opposition). They also gathered a huge amount of upvotes, meaning that the site was being flooded with these questions and that reputation was being devalued. Community Wiki was the compromise that brought these problems under control.

So, if we are being conservative:

  1. Community wiki should be used to prevent vastly unfair or gameable opportunities for gaining reputation. There will always be some easy questions that will gain disproportionate amounts of reputation, but as long as we keep the number low we will be fine.
  2. Community wiki allows valuable, but broad questions to exist on this site. One of the best guides to whether a question should be community wiki is how many different answers you would expect to get if you asked 20 (knowledgeable people). If you'd get more than 6 or 7, then it probably belongs as community wiki.
  • $\begingroup$ I know I haven't directly answered your question, just listed the principles I think should be behind CW $\endgroup$
    – Casebash
    Commented Aug 6, 2010 at 11:09
  • $\begingroup$ Yes, I like your description of general principles. But we still need a policy, I think... $\endgroup$
    – Grigory M
    Commented Aug 6, 2010 at 11:25

The only useful effect I see in making a question community wiki is to force answers to be community wiki: that is, answers should be more easily editable, or should not grant reputation. So when do we want this?

Polls or lists, explicit or implicit. Voting up or down is not a measure of how complete or correct the answer is, because those metrics do not apply to these questions. Instead, voting is used to express agreement or disagreement with a recommendation or opinion.

Questions asking for a comprehensive list of X. This would allow the top rated/accepted answer to contain a complete answer, edited whenever new answers come. I don't think there have been any like this yet, but some could eventually get converted to this format when too many answers get posted. An example.

Other possible situations:
Questions whose answers reveal little about the answerer's mathematical ability.
Breaching experiments such as this (although we shouldn't have many of those anymore)
Known open questions (these should probably go to mathoverflow or be closed instead, unless some really good answers get posted)


Okay, so I like Casebash's approach of taking SO as the template but, as Grigory says, there is perhaps more necessity for a divide here*, there is also more scope.

Certainly, as Casebash says, the broadly discursive but well motivated should be hit with the wiki hammer (and by implication, those with poor motivation are closure fodder), as should big-lists.

But notation, terminology and math history questions, as Grigory points out, provide an interesting borderline case- for my money:


  • What does the turnstile symbol mean in logic? bad question
  • Intuition for the turnstile symbol? CW
  • What is the difference between the turnstile and double turnstile symbols in logic? Rep


  • Is 0 a natural number? bad CW question
  • Why might one consider 0 not to be a natural number? good CW
  • How much of arithmetic is possible without 0? Rep

Math History

  • Who invented the integral? bad question
  • How has calculus changed since its creation? CW
  • How did Newton's definition of the integral differ from Leibniz's? Rep

Notice how it is possible to make repworthy questions in each topic, but also useless ones. In most cases the CWs are the ones that are broadly discursive, but in some cases the rep ones can be a little also. What is key is that, if a slightly discursive question requires special knowledge and care , we should offer rep as an incentive. Also if a question on a discursive topic is asking about a very specific and well defined subtopic, I feel we should deem it a fair question.

*It has been mentioned elsewhere [by @Noah Snyder?] that the proportion of people using math professionally to those using math in general is always going to be lower to the corresponding proportions of those using programming.

Edit: The problem of this question, which is both specific/well-defined and requiring no real special knowledge or care might be seen as something of a Godel number to my Principia Mathematica... That said, I think we can leave it rep and the votes will take care of it ;)

  • 1
    $\begingroup$ I disagree that we should close "Is 0 a natural number?". While it would be better to ask "Why might one consider 0 not to be a natural number?", we could always answer the question as though this had been asked. Additionally, "What does the turnstile symbol mean in logic?" seems to be a valid question. Not a particularly interesting one, but valid nonetheless. $\endgroup$
    – Casebash
    Commented Aug 6, 2010 at 13:41
  • $\begingroup$ Hmm... perhaps I was being a bit harsh. My aim (in the closure examples) was to create poorly motivated sounding questions that (probably, if the text body fit the title) would be meritous of our extreme disregard if not closure. But yeah, maybe not closed then. Will edit and adjust... :) $\endgroup$ Commented Aug 6, 2010 at 14:01
  • $\begingroup$ I have flagged them 'bad question' perhaps low votes and a note in the faq will see to it that they don't get far... $\endgroup$ Commented Aug 6, 2010 at 14:06
  • $\begingroup$ I'd say questions like "is 0 a natural number" are exactly what "close as subjective and argumentative" option for. $\endgroup$
    – Grigory M
    Commented Aug 6, 2010 at 14:22
  • 1
    $\begingroup$ @Grigory: No, CW is for "Who was the best mathematician?". Is 0 a natural number has a definite answer - it depends on the context. The asker quite possibly assumed that the answer was either a simple yes or no. In fact, I wouldn't call it a bad question $\endgroup$
    – Casebash
    Commented Aug 7, 2010 at 7:31
  • $\begingroup$ I'd like to see your Newton/Leibniz history question posted :) $\endgroup$
    – walkytalky
    Commented Aug 12, 2010 at 13:13

I think we still need a “CW-policy”. Suggestion:

  1. big-list questions, asking for sorted list of resources/books should be CW
    • and, probably, questions asking for the best example/intuition/etc in some field (including questions of most interesting propeties of some object etc)
  2. questions, that are not directly mathematical, should be CW (because answering them also shouldn't give rep):
    • notation, terminology and likes
    • math-history and likes
  • $\begingroup$ That seems significantly broader than I have seen it used on StackOverflow. Notation and terminology are quite specific questions and so usually there isn't a demand for them to be CW $\endgroup$
    – Casebash
    Commented Aug 6, 2010 at 10:02
  • $\begingroup$ @Casebash Well, probably SO has different type of terminology questions. Do you feel that people should gain rep by answering question like "is 0 a natural number"? $\endgroup$
    – Grigory M
    Commented Aug 6, 2010 at 10:07
  • 1
    $\begingroup$ @Grigory: Maybe notation and terminology questions should be CW. I would support that as long as we make a distinction between them and definition questions $\endgroup$
    – Casebash
    Commented Aug 6, 2010 at 11:16
  • 1
    $\begingroup$ @Casebash probably. could you please give an example [from the site] of definition question [that, you feel, shouldn't be CW]? $\endgroup$
    – Grigory M
    Commented Aug 6, 2010 at 11:37
  • $\begingroup$ I asked about the definition of a set. This is not a trivial question at all $\endgroup$
    – Casebash
    Commented Aug 6, 2010 at 13:12
  • $\begingroup$ @Casebash Definitely. I'd even say it's too nontrivial: different mathematicians have different opinions etc; so it's discussion question — and as such should be, I believe, CW. (Needless to repeat CW doesn't mean bad.) $\endgroup$
    – Grigory M
    Commented Aug 6, 2010 at 14:35

Some facts relevant to this question:

The effects of making a question/answer Community Wiki:

  • Lower threshold to edit: only requires 100 rep, compared to 1000 for normal posts
  • No reputation is gained for upvotes, nor lost for downvotes (this also means no -1 rep for casting a downvote)
  • The system interprets Community Wiki posts to be owned by the Community User rather than the original author.
  • All (future?) answers to a community wiki question automatically become community wiki

A question or answer becomes Community Wiki when:

  • The body of the post has been edited six (6) times by at least four (4) different people.
  • The post has been edited eight (8) times by the original owner.
  • The post's author checks the community wiki checkbox when composing the question or answer. Note: this feature is not available to users with <15 rep
  • The question generates more than n answers (I think n is 30 here, but it might be 15)
  • The answer is posted in response to a community wiki question
  • The original author or a moderator edits the post and checks the community wiki box.

Other important information:

  • Community Wiki mode is irreversible.
  • Although reputation from votes is not counted, badges are still awarded as normal.
  • Any reputation changes before a post becomes community wiki stay.

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