# Many (historical) duplicate questions - how to pick a “canonical” question?

I want to bring this up here rather than mass-flagging a whole bunch of questions as duplicates (and also avoiding the issue of choosing one as the "base")

This question from today is a new member of a group of many questions (a b c d e f g and probably more) all with slight variations between them. In a case of a single duplicate of a prior question, what to do is quite straightforward. But in this case, there are numerous historical duplicates, quite a few with (broadly the same) good answers, though none have really addressed the topic in its entirety - thus providing additional difficultly in determining which one should be "promoted" as the primary question. Potentially there could be mergers here as well?

Should I just go ahead on a flagging spree and let the moderators sort it out?

A. There's a number of levels of association of similar questions
$\quad$ (4 by my reckoning, if we also count 'not quite similar enough to do anything'):

1. Where the questions are exact duplicates, to the extent that they invite identical answers - and both have answers - they should usually be merged (preferably into the better question; if they're of similar quality, merge into the older one). If they don't both have answers, treat as 2.

2. Where the questions are asking the same thing - to the extent that answers to one will solve the other question, but the answers themselves don't really answer the other question, one should close as duplicate; again the better/more canonical question should normally survive, though the quality of answers and age are other factors to consider.

3. Where the questions come close to asking the same thing, but in a different way -- in a way that invites questions that to some extent explore different aspects of the issue -- then they should probably both stay open, but be linked (both ways) via comments. See this earlier post for some discussion of that issue (see the Jeff Atwood quote in particular)

B. I suggest doing it in stages

1. I suggest taking care of flagging any you think should merge first.

2. Then depending on your privileges, either vote to close as duplicate or flag the ones that should close as duplicate.

3. Then link (via a comment in each) any that should still stand separately but where the answers to the other question may still be useful.

[I'd also suggest that with wholesale flagging, to avoid overwhelming the flag queue -- about half a dozen flags at a time is no problem, but two dozen in a day on the same thing (some people can do that many) might lead to missing a more urgent flag (such as a spam flag). If it's a lot, spread it out a bit. This also has the advantage that if posts do get bumped, the front page isn't full of old questions all on one topic.]

• (+1) With levels 2 & 3 it's sometimes helpful to briefly explain why the duplicated/linked posts are related, when this might not be obvious to everyone. – Scortchi - Reinstate Monica May 12 '15 at 9:23
• +1 @Scortchi excellent point; indeed, giving an explanation when flagging is often a big help. – Glen_b May 12 '15 at 9:26

I have been reviewing a large number of older questions some months ago (I went through the [pca] tag in its entirety), trying to tidy them up and systematize as much as possible. I have encountered a similar situation a couple of times. @Glen_b gives good general recommendations in his answer, but I think I can make several more points:

1. Everybody agrees that it's good to have a "canonical" thread with clearly and concisely formulated question and high quality answers. Try to find a candidate thread among all near-duplicates. Some things to consider:

• It does not have to be the oldest question;
• It should better be well-upvoted (to increase visibility);
• It should be concisely (!) and clearly formulated;
• If there is an accepted answer, it should better be good;
• You can edit the question to make it better.
2. If such a thread exists, edit it to make it as good as possible. Pay special attention to the title and the tags.

3. Check if some other threads contain answers that could be moved into this canonical thread. Is so, flag those for moderator attention and suggest to merge; make sure to explain why (otherwise moderators might not get what you are after and will refuse to act upon your flag). Note that only relatively rarely can answers be seamlessly moved between threads.