Sometimes users leave comments on questions that are essentially a short answer to the question. What is wrong with answering a question in the comment section? Is it ever appropriate to leave an answer in the comments?
Answers to questions should be posted as an answer, not a comment.
What is wrong with answering a question in the comment section?
Stack Exchange websites are sites focused on questions and answers. They have a lot of community features that make them better than other types of sites:
Questions and answers can be edited (improved) later, either by the original poster or anyone else that has an improvement.
Questions and answers can be upvoted and downvoted by users, ensuring that the best information is at the top.
Users can ask questions about the answers, asking for clarification or refuting information, by leaving a comment for a specific answer.
Reputation can be earned for good posts, and lost for bad posts.
Answers are essentially permanent; they are generally only deleted by a moderator if they are not appropriate for the question. Even after they are deleted, they are still visible on the site for high rep users and can be undeleted if necessary.
The person who asked the question can select the answer they thought was the most helpful and accept it.
When a new answer is posted, the question is bumped to the top of the front page, notifying everyone about the new answer and inviting community moderation.
Posting an answer in the comments breaks all of these features:
Comments cannot be edited by anyone, even the user who left the comment.
Comments cannot be downvoted and are sorted by post date, not by score.
Although you can leave a response for a commenter, comments are not truly threaded, and you can't leave a comment on a comment.
Reputation is not changed for good or bad comments.
Comments are intended to be temporary. If there get to be too many comments, moderators will sometimes delete all the comments or move them to chat. My understanding is that moderators have a "Purge Comments" button, which tells you how easy it is for comments to be deleted.
Comments cannot be accepted by the OP as the best answer.
New comments do not bump the question, which means that comments get less attention than new answers.
It can be tempting when you see a new question that doesn't have any comments yet to leave a one-sentence answer as the top comment. That way, you get your opinion in early, your post will always be first at the top of the page, and you don't have to worry about anyone downvoting your "answer." But that is not how this site is supposed to work, and doesn't leave your "answer" open to the community moderation features.
Is it ever appropriate to leave an answer in the comments?
Sometimes people think that a one-sentence answer is too short to be posted as an answer. If you are saying so little in your answer that it is too short to be posted as an answer, you should ask yourself if there is any value in posting it at all. If you are essentially leaving an opinion without providing any justification for that opinion, perhaps you should upvote a different answer instead of posting your own. If you don't have time to post a better answer, then wait until you do have time. On the other hand, perhaps the question is simple enough that a short answer is enough; if so, post it as an answer.
Occasionally, you might ask the question asker for clarification, and in the process stumble upon the answer in the comments. At that point, you should write an answer and post it as an answer. Here is an example of a time that I did this on a different SE site.
What if I'm not sure if my answer is correct, and I'm only speculating?
If you aren't sure of your answer, it is even more critical that you post it as an answer, not a comment. The reason is that you need to allow your possible answer (which may or may not be correct) to be moderated by the community. Other users should be able to vote it up or down and to leave comments explaining why it is or is not correct.
What if it is a link-only answer?
The reason link-only answers are discouraged is that they have a tendency to become worthless when the link goes dead. Posting these as comments is no better than posting them as answers. In fact, it is worse; as an answer post, the link has the possibility of being edited in the future if necessary, but as a comment, it can never be edited.
Instead, feel free to post your link in an actual answer post, just be sure to include a summary of what the reader will find on the other side of the link that answers the question.
EDIT - We have an example in the wild that raises an issue tied to this question. Friend was brainwashed with MLM-/ponzi investment scam. What can I do? had a comment -
Go to the police. This is fraud and is illegal. Sure, this will hurt your friend but better now then when he starts abusing of his position to fraud even more people...
Which another, new, member copied and posted as an answer. Another member flagged it to the mod's attention. Ganesh and I discussed it, and agreed that if the answer is simply a copied comment, it should have attribution to the comment author. If it's turned into an edited, expanded, comprehensive answer, attribution may not be as big a concern. Is this approach satisfactory?
For sake of my 'answer', let's assume I agree, and start with No (as I agree with your concern).
The real question may be, "How should we handle comments that are really answers?" Right? Else, we simply agree with you, but have no consensus how to handle this.
The option for a mod to "convert to answer" doesn't exist, we do not have that option as we do for "answers that are really comments," that we just flip to a comment on the OP question. The implication here, is that a flag on such a comment is really a request to delete it.
Another option is that a member take the ball and run with it, copying the content, and hopefully adding a bit to it, to make it a good answer.
Third choice is for a further comment to prompt the OP to change it to an answer himself. This is what I typically do, and more often than not, it happens.
My concern is the gray area. One example offered in another answer was a link-only answer. That answer would be voted down as link-only, or converted to comment. But here, it seems that some would consider it too-good-for-comment. Which then will just lead to more discussion on something that I haven't seen as a major issue, yet.
Update - I wrote myself a macro for a comment reply for this issue -
Fill in member name - this comment is "too good to be a comment" - please consider deleting it, and write it as a full answer to the question. See the meta question Should answers be left in the comments? for more details.
I just used it at Rent at $1500/month in Toronto or Mortgage even with ≥ 5% interest? and the OP complied. (The example in the wild is now deleted)
Please comment below if you have any advice to improve this line.
See past discussion.
In principle you are correct, answers belong in answers.
In practice there will always be disagreement whether something is a comment or answer, with no reliable line between them. Reality is fractal; human behavior more so.
If you really think a comment should be an answer, you are free to turn it into one by quoting it in an answer of your own (properly credited, preferably). If it isn't worth your effort to do so, it isn't worth complaining about; accept that the world is imperfect and let it go.
(I should also point out that the short responses you say should be Answers often draw complaints about "that should have been a comment." Unless you want people to stop contributing entirely, there is no perfect solution here. It's working well enough. Let it work.)
A comment that is clearly an answer should be deleted, full stop. Comments are not appropriate locations to give answers. Answering questions in the comments is harmful for the site; it ends up with questions that go unanswered, and it ends up with people thinking the site should work more like a forum.
A comment that gives the appearance of an answer but might be understood not to be sufficient for an answer... also should be deleted, if it's just answering the question and not clarifying the question. Comments are for clarifying the question.
So, for example, here:
Q. How can I do my taxes online?
C. The IRS has a page to help you out, www.doyourtaxesonline.com.
That's an answer, and should be deleted.
Q. How can I do my taxes online?
C. Have you seen www.doyourtaxesonline.com?
That's not helping clarify the question - it's more-or-less an answer. Whack.
Q. How can I do my taxes online?
C. Are you looking for something like www.doyourtaxesonline.com?
That's potentially clarifying, so it's fine - but I'd remove it once the clarification is received, and the comment poster has a chance to post it as an answer if that is indeed what they're looking for. This is what I'd consider a 'borderline' case.
Q. How can I do my taxes online?
C. What country are you in?
That's clearly a clarifying comment, and should stay until the clarification is received and then be subject to removal, as with any other now-irrelevant comment.
I imagine the point is clear: I support keeping comments as clean as possible. If they're clarifying something with the OP, they should be kept until that clarification is received. If they're chatting, answering, maybe-answering, or anything else, they should be removed whenever a mod is around who feels like removing them (or moving them to chat if appropriate).
The incentive already exists to leave an answer rather than a comment. Comments can get upvotes but no points are awarded. Similarly comments cannot get downvotes. Would a downvoted comment have sufficient penalty if there are no points deducted?
Comments can be deleted without moderator attention if 3 (+ the number of upvotes) users flag them, that's lower than the threshold for close votes. The problem with an effort to enforce this rule is that unless multiple users are flagging comments all the time, this falls on the moderators. Unless there are enough users committed to policing comments, then we won't likely see progress here.
I agree with others who have mentioned that the line between a good answer and a helpful comment is pretty fuzzy, and I don't agree that comment answers are terribly harmful. I think a good answer with upvotes deters other answers more than a comment answer does. At least a comment answer can point a user in the right direction even if it doesn't take the time to fully explain why.
All that said, given the lower value of comments on stackexchange, deleting comments will probably hurt less feelings than deleting answers and closing questions.