Question Mark (?)
The Basics

[1] Direct questions
     
              Where did she go
?
              Did he catch the bus?

[2] Questions embedded within a sentence

              How far can he run? she wondered.
              (notice, "she" is not capitalized.)

[2A] but is not used in an indirect question

              She wondered how far he could run.

[3] A series of questions within the same sentence

              How is your health affected by smoking cigarettes? drinking alcohol? eating trans fats?

[4] Can be used to turn a declarative statement into a question

             You don't mind if I borrow your car?
              You're not sad?

Beyond the Basics

[5] Rhetorical questions: the question mark is optional

              What is the point.    (Rhetorical and pessimistic)
              What is the point
?   (More interrogative than rhetorical)
              What is the point!    (Rhetorical and possibly argumentative)
              (All three are grammatically correct.)

[6] If a command is phrased, for politeness, as a question, but is still essentially a command, no question mark is used

              Will you please turn down the stereo.  (as spoken by a mother to her son)

[6A] But if it's really a question, then use a question mark.

              Will you please turn down the stereo?  (when spoken as an earnest question)

Stylistic usage

[7] A question mark can be used to create a feeling of stream of consciousness

              Was your vacation everything you hoped? Did you meet a cute guy? learn to surf? sunbathe nude?
                     
Syntax

No spaces before, one space after.

If a direct question is preceded by an introductory phrase or clause, the first word of the question may be capitalized (but doesn't have to be).

              We must ask ourselves, Can the stock market be beaten
?
              You have to ask yourself, was it worth it?
     
              (Note: Capitalizing the first word adds a formal feel to the sentence)

A question mark should be placed inside quotation marks or parenthesis only when the quoted or parenthetical matter is a question

              David asked, "Do you like me
?"
              Was she crying when she said, "I hate you"
?
             
Let's see how the pros use it

Naturally the question suggests itself, Why did these people want the river now when nobody had wanted it in the five preceding generations?
--Mark Twain (Life on the Mississippi)

In any of the burial-places of this city through which I pass, is there a sleeper more inscrutable than its busy inhabitants are, in their innermost
personality, to me, or than I am to them
?
--Charles Dickens (A Tale of Two Cities)
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