All over the the internet, and especially on SE sites, I see the following construction in the titles of questions:

How to write a question?

How to make a widget?

How to add foo to bar?

After some digging, I was able to find this previously answered question: Is a question beginning with “How to” grammatically correct?

Both answers offer some insight, but I'm looking for details regarding the correctness of the "sentence" when it includes the question mark, something @Kris mentions briefly that I still don't understand. He offers the example:

I don't have the manual now. How to fix my computer?

and says this is a grammatical sentence since the bolded part is used in context. Is this really grammatical? Both @Barry England and @Kris agree that this phrasing shouldn't be used in formal writing, but I can't think of any situation where (as a native speaker) I would use this even in informal speech. I would never say to a friend:

How to turn on your TV?

All three examples I gave earlier seem perfectly acceptable as titles for instructional articles on the topics when the question mark is removed:

How to write a question

How to make a widget

How to add foo to bar

but I can't help feeling that something is off when I see these titles with a question mark at the end.

Shouldn't they be written like this instead?

How can I write a question?

How is a widget made?

How is foo added to bar?

  • If this question is not distinct enough from the one I linked, please let me know how I can improve it. I tried to be fairly specific. – arbitrarystringofletters Dec 30 '16 at 15:27

A sentence usually has its subject and verb. However, there are so many cases where you just drop both or either of them because (1) you don't need both of them as in an imperative sentence, (2) there is some supporting context and (3) you don't have enough space as in headlines, e.g., What to Expect From Trump's First 100 Days. Is this example grammatical? Of course, it is. It could be short for

Those things that you can expect from Trump's first 100 days.

I will tell you what to expect from Trump's first 100 days.

If you place a question mark after the two sentences, it won't be grammatical because they are not interrogative sentences. You place it only when a sentence is interrogative.

How to write a question?

Is this clause (phrase) interrogative? Yes and no.

Yes, when it is short for

Can you tell me (teach me, explain to me) how to write a question?

No, when it is short for

I'd like to know (ask you) how to write a question.

Which one sounds more natural and idiomatic? It's very difficult to answer this question, but probably it will depend on context and your intention. In other words, do you want to ask a question? Or do you want to answer it with some explanation?

As the two answers indicate, they are grammatical. Regarding your last question, "Shouldn't they be written like this instead?" the answer could be "It depends."

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