# How to write a good MathOverflow question?

How do I write a good MathOverflow question? Got any advice for me?

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In the interest of making this great advice more visible, is it possible to add this to the "featured" list of meta questions and make a link to this visible from the "Ask question" page? –  j.c. Aug 26 '14 at 16:39
@j.c. the featured tag expires after a while. We could renew it every time it goes away but there ought to be something better... –  François G. Dorais Aug 27 '14 at 1:09
@FrançoisG.Dorais I assume you could (at least if you ask SE) include that advice in mathoverflow.net/help/how-to-ask (which is linked from the grey box on the "ask" page), and/or you could ask for an additional link from that box (or for a change of the target of the existing link). [Tangentially, AFAIK self-accepts do not influence ordering.] –  quid Sep 2 '14 at 8:53

Using MathOverflow should be an extension of the way you normally do mathematics, and the same rules you use to effectively solve problems can be used to make good MO questions. Just like solving problems, crafting good questions requires you to put in some effort!

• Ask a focused question that has a specific goal
• Be precise
• Break it down
• Consider different formulations of the question
• Provide background and motivation

## Ask a focused question that has a specific goal

It should be absolutely clear what constitutes an answer to your question. Here are some examples of vague and specific questions. For each one, ask yourself, "If I saw an answer to this question, could I confidently determine whether it tells the asker what she actually wants to know?"

• What can I deduce from X?
• What is known about the X conjecture?
• What are all the ways to do X?
• Tell me about elliptic curves.

Focused

• Does X imply Y?
• Is there an example of X such that Y?
• Is the X conjecture true in situation Y?
• Is there a way to do X other than Y (which I can't use because Z)?

Note that being specific does not mean plugging in specific numbers or otherwise making your problem look like an exercise in a book. It means asking a to-the-point question that has an answer.

## Be precise

Being precise means communicating the parameters of your question so that others know where to start answering it and know when they've given you a complete answer. Of course, the includes stating the hypotheses and goal of your problem. If you suspect that you're asking an elementary question outside of your field, you may also want to explain your background a bit. This makes it easier for the person answering your question to know what she can take for granted.

It is especially important for "soft" questions and "big list" questions to be precise. Otherwise they'll be boring and useless. "What are the best number theory books" is a bad question. Best for what? Assuming what background? A better version of the question might be "What are the best textbooks for an undergraduate number theory course?" or "After an undergraduate number theory course, what should I learn if I want to study elliptic curve cryptography?" These questions aren't great, but they make it clear what the starting point is and what the goal is.

Make sure it's clear exactly what your question is. It's extremely frustrating to read a long question which explains what the general problem is but doesn't contain an actual question. I usually resort to searching the body of the post for question marks, but it often doesn't help. After defining all your terms and motivating your question, consider visually distinguishing the final version of the question (see the formatting section).

Before asking your question, try to solve it. Search Google, Wikipedia, and nLab, check any references you can think of, and try to figure the problem out yourself (maybe even sleep on it). Doing so will help you break the problem down and understand it better. Even if you don't solve the problem, putting some work into it will often help you understand exactly what it is you're having trouble with, so you'll be able to ask a better question.

## Break it down

You may have a specific problem you're trying to solve, and you may have done your research, but the problem might be a monster. Even if it's not a monster, you'll probably benefit from trying to break the problem into smaller pieces and posting one or two of the pieces on MO. To modify a quotation of Pólya, "If there is a problem you can't solve, then there is an easier problem you can't solve: find it." You may worry that the the pieces are not interesting enough or are too specific to post on MathOverflow, but you shouldn't. It's much better to post a question that is too focused than to post a question that is too vague or too broad.

It's okay to ask several questions related to a project you're working on, but try to limit yourself to one or two per day. Rather than posting all the parts of your problem at the same time, work through them one at a time. After all, the solution to one part may completely change your plan for solving the problem.

## Consider different formulations of the question

Sometimes your question is boring, but you can often make it much more interesting by recontextualizing it.

## Provide background and motivation

(But don't forget to restate it in the body!)

Use your title to convey as much information about your question as possible. Since the tags already convey the general subject area of your question, the title should communicate the question itself as faithfully as possible. If necessary, leave out hypotheses in the title, and in the body of the question, explain why the question requires those hypotheses.

Don't be afraid to make your question title long. Titles are allowed to be anywhere from 15 to 250 characters long. 140 characters (the length of a tweet) takes up about two full lines on the home page, so try to keep it less than that. But 140 characters is a lot longer than you might think. Too many people restrict themselves to 20 character titles. They're trying not to waste your time by making you read a long title, but they end up wasting more of your time because you have to actually open the question to see if it's interesting to you.

The readability of your question can often be greatly improved if you learn to use formatting commands, especially if your question ends up being quite long. Here is an example that contains a few good uses of the formatting commands:

## Background/Motivation

A *doodad* is a thingumabob together with a sheaf of doohickies (which is usually called the *doo structure* on the doodad). A doodad is said to be *regular* if the sheaf of doohickies is regular. Intuitively, regularity makes a doodad "rigid" since information about the doo structure at a point can be translated into information about the doo structure at nearby points.

A *widgit* is a whatsit which is flat (in the sense that its Plotsky curvature is zero). Showing that a space has a widgit on it is extremely useful because the flatness allows you to apply Foobar's gadget construction to prove many useful results about the space.

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Based on the above intuition, it is natural to ask if every doodad is a widgit. However, the answer is clearly no, since a widgit is always regular, but [some example] is a non-regular doodad, so it is clear that we must impose a regularity hypothesis.

> Is every regular doodad a widgit?

## Background/Motivation

A doodad is a thingumabob together with a sheaf of doohickies (which is usually called the doo structure on the doodad). A doodad is said to be regular if the sheaf of doohickies is regular. Intuitively, regularity makes a doodad "rigid" since information about the doo structure at a point can be translated into information about the doo structure at nearby points.

A widgit is a whatsit which is flat (in the sense that its Plotsky curvature is zero). Showing that a space has a widgit on it is extremely useful because the flatness allows you to apply Foobar's gadget construction to prove many useful results about the space.

Based on the above intuition, it is natural to ask if every doodad is a widgit. However, the answer is clearly no, since a widgit is always regular, but [some example] is a non-regular doodad, so it is clear that we must impose a regularity hypothesis.

Is every regular doodad a widgit?

Notice that the background/motivation is clearly labelled with a section header and clearly delimited by the horizontal rule, making it easy for experts to know what to skip or skim. The words being defined are italicized. After the nuances about why the question introduces some hypotheses, the precise final question is visually distinguished in a blockquote, making it easy to know exactly what constitutes an answer to the question.

## A final note

Not every piece of advice on this page may apply to your problem, and it may even occasionally happen that you can make your question better by violating some rule laid out on this page. As with any writing you do, it is important to know what the basic rules are. If you violate one of them, it should be a conscious choice and you should be doing it for a very good reason.

• Eric Raymond's How To Ask Questions The Smart Way is directed at people looking to post problems to computer software/hardware forums, but much of the advice applies to asking questions on MathOverflow as well.

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The advice "Make your title your question" is good in my opinion. However, what I find unfortunate is if users then do not repeat the question in the body. Could a phrase be added there, like: 'Yet please also make sure that the body of the question does not depend on the title, and thus in any case also state the question in the body.' (This is not mainly about people sayin 'question is in title' though I find this somewhat onfortunate to, but some say strictly nothing on the q in body if it is in title.) –  quid Oct 12 '13 at 14:42
It would be cool if in addition to saying "Just read Wikipedia for X; don't ask here" you could elaborate on the etiquette of asking here. Theoretically people can just ignore bad questions. But since this isn't the attitude, there has to be a reason. –  isomorphismes Sep 11 '14 at 8:02
@isomorphismes, I'm not sure what you're asking for. Who says "Just read Wikipedia for X; don't ask here"? A reason for what? –  Scott Morrison Sep 11 '14 at 23:17
Btw, every regular doodad is in fact a widget. –  mdg Sep 17 '14 at 7:39
@ScottMorrison In the Do your homework section you said do basic googling before asking on MO. Sorry, by "a reason" I meant to say "There has to be a reason that people [a] answer questions and [b] are annoyed by, rather than simply ignore, bad questions". I'm presuming that [a] and [b] spring from the same source, which is tied up in the norms which probably a lot of MO users understand, but I don't as well without it being explicitly described. –  isomorphismes Sep 17 '14 at 8:38
@isomorphismes, I think the best summary of etiquette for asking questions is 'visibly have put in effort to follow the above advice'. –  Scott Morrison Sep 17 '14 at 23:09
Your sample question abuses the > formatting tag (originally meant for quotations) to highlight text. It is a common strategy here, and I have been guilty of using it myself occasionally, too. But do we want to explicitly suggest and encourage it? –  Federico Poloni Sep 25 '14 at 9:25
Why not? It looks nice, I think. (It's not like markdown promises to indicate semantics.) –  Scott Morrison Sep 25 '14 at 21:25

If you ask a question you're asking a favor (the eventual award of MO-points does not change this fact). This means that you should give the public something in return. The formulation of the question should not be egoistic, just for sake of getting an answer. Within reason, you should educate MO-public about the topic. Thus the formulation should be as self-contained as possible. One should state the relevant definitions, and even in two ways--descriptively (say: fixed point $x$) and formally (say: $\ f(x) = x$). Then it is easy to read a question with a pleasure (and to understand the question in the first place), and it is also possible to check the mathematical detail.

A question should be addressed to as wide MO-audience as possible, and not to a narrow circle of the exact specialists. Furthermore, when the question is written to a wide audience than the chance for receiving an answer often increases dramatically. It is likely that a sharp mathematician will provide an answer without being an actual expert in the given narrow field.

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MO seems to be a place where a differential geometer may ask about general topological manifolds, a topologist about algebra, etc. (and everybody would love to ask about logic if they were not afraid :-).

Thus in my opinion the homework should not be stressed too much. Instead, one should aim at mathematically interesting questions. And this means--not ignorant. Interesting.

Otherwise MO would tend to be... boring :-)

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+1. I agree with this very much. (But I don't understand your remark about fear of asking logic questions.) –  Joel David Hamkins Sep 18 '14 at 22:51
@Joel, thank you. (I was just joking about questions about logic). –  Włodzimierz Holsztyński Sep 18 '14 at 23:00

A question (or an answer) is an exercise in communication. Thus the well known general suggestions will work most of the time, be it mathematics, prose, poetry, ... (granted that there are exceptions). For instance, the sentences should be preferably simple (not compound) and short.

My oooold advice is: keep pronouns to a minimum. Use explicit nouns. Most of the time it is better to repeat the same noun than to replace it by a pronoun. Pronouns often make a sentence hard or impossible to parse in a unique way, they may even mislead a reader.

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I prefer pronouns. I usually prefer professionals over hobbyists, and pronouns are professional nouns! This in contrast to your answer which is pro-nouns and against pronouns! –  Asaf Karagila Sep 18 '14 at 22:54
@AsafKaragila this is profound! –  magma Sep 21 '14 at 23:17
@magma: It is indeed. And I'm pro profound, as I said, I prefer the professional found words, over the hobbyist found words. And where a pro would be profound, a hobbyist will usually only be found. –  Asaf Karagila Sep 21 '14 at 23:23
@Asaf, you value word games more than words. –  Włodzimierz Holsztyński Sep 22 '14 at 0:33
It's an illness really. I'm the victim here... :-) –  Asaf Karagila Sep 22 '14 at 3:55
A victim? I'd rather say that you're guilty as charged :-) –  Włodzimierz Holsztyński Sep 22 '14 at 4:48