Question Mark with a Brief Afterthought Expression
The Question Mark
Rulebase Summary
When a question has a brief afterthought tacked on that won't be misread (such as 'if you remember', 'if you recall', 'if you know'), separate the afterthought with a comma and end the entire sentence with a question mark.
However, if the afterthought uses 'can' or 'do' instead of 'if' (making it a separate question in its own right), end the main question with a question mark and start a new sentence for the afterthought.
Other kinds of fragments added after a question may begin with a capital letter as a separate sentence.
Examples
Q. Where was the vehicle parked. If you recall.
Q. Where was the vehicle parked, if you recall?
Brief afterthought joins with comma — one ? at end.
Q. What color was the truck, do you remember.
Q. What color was the truck? Do you remember?
"Do you remember" is its own question — separate sentence.
Transcript Notes
The critical distinction is whether the afterthought uses "if" (which joins the question with a comma and a single question mark at the end) or "do" or "can" (which creates a separate question requiring its own question mark and a new sentence).
Style Guide References (2)
Morson's
BGGP