I'm afraid this question itself is very likely to be a duplicate, but I haven't been able to find this information by searching Meta.

How exactly does the system decide when to close a question as a duplicate?

I know a question must be closed in order to be a duplicate. Moderators and users with a gold tag star can do this unilaterally. Regular users must put in 5 close votes.

The FAQ page "How should duplicate questions be handled?" says:

If five close-voters agree that the question is a duplicate, or if the asker agrees, or if a sufficiently privileged user votes to close, then the question will be closed as a duplicate.

But in my experience, the question can be marked as a duplicate even some of the close votes are for a different reason. I'm not sure, but I think it just requires a majority (three users) to agree that the question is a duplicate.

I've also seen cases where a question is marked as a duplicate of more than one other question. For example: Which is correct — “a year” or “an year”? How did this happen? Is it still possible, or is it some relic of an older system for closing as duplicate? Since it seems people can only vote for a single duplicate, I'd assume this means different users made different votes. Am I right? I'm not sure what the numerical requirements would be for this--does this happen if at least two users vote to close a post as a duplicate of one question, and at least two users vote to close it as a duplicate of another? After looking more closely, I noticed the second duplicate target is marked as a duplicate of the first. So my best guess is that this happens when the target of a duplicate becomes marked as a duplicate of another question.


Generally, the close reason supported by most voters wins. Exception: users with a binding vote (moderators, gold tag badge holders in case of a duplicate) overrule others.

When there is a tie, the time when a vote was cast is used as a tiebreaker: later votes have more weight since they are likely based on a newer revision or additional comments.

When there are multiple duplicate targets, all of them are listed in the duplicate banner on top of the post. All duplicates are counted together toward "close as a duplicate" reason. So, if 2 people vote to close as a duplicate of question A, 1 votes as a duplicate of question B, and two vote as unclear, the question gets closed as a duplicate, and both A and B are listed on top of the question.

Whether the targets (A or B) are themselves closed as a duplicate makes no difference here.

See also: Close Vote Reason Logic When There Isn't a Majority

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  • Thank you. I'm wondering if the answer to the question you linked to is up to date. The quoted section of the FAQ page "What is a “closed” or “on hold” question?" was removed in 2013 by Robert Harvey for apparently unclear reasons. – user306255 May 3 '16 at 16:35
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    As a note, apparently votes to migrate require three votes regardless and four on SO. meta.ell.stackexchange.com/questions/3062/… – Catija May 14 '16 at 1:30

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