Inclusion or exclusion of a question mark is usually a straightforward matter. However, there are instances in which what are framed as questions should end with other punctuation, and occasionally, a statement might be followed by a question mark. A discussion of exceptions to basic use of the question mark follows.
Questions are statements of inquiry intended to elicit a response — for example, “What is the matter with you?” — but not all inquiries or seeming inquiries are, technically, questions.
Depending on context, a sentence may or may not merit a question mark. For example, the rhetorical question “You didn’t break my antique vase,” uttered in an alarmed tone after the speaker has witnessed that very action, would be voiced with downward inflection. The speaker is not asking for a response; he or she is essentially thinking out loud while processing the traumatic incident.
But if the speaker asks someone to confirm that his or her suspicion of the other person’s complicity is unfounded, he or she would ask, with an upward inflection, “You didn’t break my antique vase?”
In a declarative or imperative sentence expressing disbelief, doubt, or surprise, a question mark is acceptable: “This is what it has come to?” However, an exclamation point can preempt a question mark in an emotionally expressed question: “How do you know that!”
Indirect questions, like “I wondered what she was talking about,” should not end with a question mark. Likewise, an exclamation that superficially appears to be a question — for example, “Was she ever surprised!” — is just that: an exclamation.
Question marks should not follow questions that are disguised requests: “Could you please close the door on your way out.” (In writing, such requests are best rendered more concisely: “Please close the door on your way out.”)