Q. How should the sentence “Guess what” be punctuated? I realize that it’s technically an imperative sentence, which should end with a period (or exclamation point), but in many contexts it’s used as if it were interrogatory, and thus it’s often punctuated with a question mark rather than a period. Is this simply incorrect?

A. I think the question mark is incorrect when the imperative is intended, although as you say it is common and accepted. The reason I would quibble is that using the question mark for the statement or exclamation doesn’t allow us a way to differentiate the actual question when it is called for, as in the following examples.

“Go ahead and guess,” she challenged. “Guess what?” I asked.

“Guess which variable’s value is estimated as a function of the independent variables,” demanded the professor. “Guess what?” I stammered.