Tags on SE can be made synonyms with or without merging.

Non-merged synonyms have a bit of a weird behaviour. Take a look e.g. at which is a synonym of . If I search for [books], I get redirected to the search for [references], and the questions tagged with [books] are included into the search, try https://stats.stackexchange.com/questions/tagged/books (880 results). If somebody writes a question and tags it with [books], it will automatically be re-tagged to [references] at the moment of posting. If somebody edits an old question tagged with [books], it will automatically be re-tagged to [references] too. If I see a question tagged with [books] and mouse-over this tag, I see tag wiki excerpt from [references].


  1. questions tagged with [books] are still displayed with [books], and
  2. if I browse https://stats.stackexchange.com/tags, I see [references] with only × 713 question count and [books] appears with × 168 question count and its own tag wiki excerpt (which can be seen pretty much nowhere else) --

and both of these things are somewhat annoying.

"Merging" simply means that all the questions with [books] are silently and instantly re-tagged to [references]. According to the meta.SE thread What are tag synonyms and merged tags? How do they work? (emphasis mine),

All good tag synonyms should eventually be merged (source). This retags all questions tagged with a synonym – which is not automatically done when a synonym is created. As merging is not (easily) reversible, it should be done with caution and only when a synonym is established. Only moderators can perform a merge.

So, shall we be merging all our "established" tag synonyms? How should we define when a synonym is "established" enough? I would say 1-3 months trial period after a synonym is created should be enough. If so, should we go over all existing synonyms and do the merges?

There is even a special tab for the un-merged ones on the tag synonyms page, clearly indicating that the SE system is inviting the mods to do the merges:

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    $\begingroup$ Some of these seem a bit odd: e.g. (statistical) quality-control is broader than control-chart, encompassing acceptance sampling, measurement systems analysis, & design of experiments. But if the synonym's a good one, I can't think of a reason for not merging. $\endgroup$ Commented Oct 26, 2015 at 13:26
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    $\begingroup$ Is this suggestion also valid for synonyms on CV Meta? $\endgroup$ Commented Oct 30, 2015 at 23:29
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    $\begingroup$ @Andre, Yes, why not? $\endgroup$
    – amoeba
    Commented Oct 31, 2015 at 10:38
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    $\begingroup$ Next election I will vote for you as a moderator (if you nominate yourself), because all the good work you have done; and because I would like to see all those synonyms (in main and meta sites) merged :) $\endgroup$ Commented Mar 27, 2017 at 14:01
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    $\begingroup$ @AndreSilva Haha. I would not be a very good moderator candidate; one reason is that I am trying to decrease my participation, another is that I have never been working on the review queues. But perhaps we could/should have a designated "tag mod" :) $\endgroup$
    – amoeba
    Commented Mar 27, 2017 at 14:09

1 Answer 1


Should we be merging our non-merged tag synonyms as a matter of course?

Yes, we should.

The answer is in your question, which reflects the Stack Exchange guideline towards merging synonyms (What are tag synonyms and merged tags? How do they work?): "All good tag synonyms should eventually be merged".

How should we define when a synonym is "established" enough?

Let's say, give two months to users realize a synonym was implemented, and one additional month, so any objections can be made. If nobody presents concerns about the synonyms in 3 months, then, merge tags.

So, for example, according to this proposal all tag synonyms in CV Meta should be merged right away, because the newest non merged synonym is from May/2015.


One advantage of carrying on such mergings is to help users progressing towards tag badges (while just synonymizing them won't) and this is good because users with gold tag badges gain the close/reopen duplicate binding vote privilege [only] over questions with those tags.

See this post on Meta Stack Exchange and the answer from animuson's. He says:

Conduct the merge so there are no longer questions tagged with the synonym. Once all the questions have been retagged by the merge, your tag score will transfer to the new tag when the recalc runs and the old synonym tag will no longer be eligible for tag badges ... .

So, for example, @gung should have already been awarded a bronze tag badge for the tag in CV Meta, because he has +231 score in 23 answers and there are 101 questions 'tagged' 1, but actually it has two non-merged synonyms and , so making it officially not 101 Q, but 91 [on-topic], 4 [close-reasons] and 6 [scope]. A merge would solve this.

'But how do we know if tags were merged or not?' According to this answer from @Wrzlprmft, we should see no tags in this page.

1A user eligible for a bronze tag badge should have at least score +100 in the tag, a minimum of 20 answers in the tag, and that tag needs to be used in at least 100 questions.

And as @Glen_b points out merging synonyms can also cause dropping of redundant badges. For example, four tags which are synonyms are merged, and a user had bronze tag badges in all of them (100 votes spread in 20 answers for each tag) before the merge. Then, after the merge the user will keep only one bronze tag badge (for the master tag), and will gain a silver tag badge (400 votes spread in 80 answers in the master tag).

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    $\begingroup$ You mention merging helping people progressing toward badges ... but one disadvantage of merging is that it can remove badges from people that have already earned both; that's unlikely with gold badges but it definitely happens with lower badges. I have lost badges in merges and I expect other high reputation users have as well. [not that it's so very important in that the people impacted probably don't care so much about losing the odd badge compared to the larger number who will gain badges, but it's worth keeping in mind that there's another side to that equation]. $\endgroup$
    – Glen_b
    Commented Apr 5, 2017 at 22:46
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    $\begingroup$ I am marking this as accepted now because it seems that nobody disagrees and because today @gung merged a whole bunch of older synonyms. On Meta there are no unmerged ones left. On the main site there are still some old ones to merge; hopefully they will be taken care of soon too. $\endgroup$
    – amoeba
    Commented Feb 20, 2018 at 21:53

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