"That's Dad's boss!" Ron breathed. "Cornelius Fudge, the Ministry of Magic!" Harry elbowed Ron hard to make him shut up.
…
Before Fudge could answer, there was another loud rap on the door. Dumbledore answered it. It was Harry's turn for an elbow in the ribs; he'd let out an audible gasp.
Harry potter and the chamber of secrets.
I searched the difference between "did" and "would", and found out that "did" just indicates a fact, whereas "would" includes person's will. (I saw this one.)
But I'm still confused. Then here, "he would let out a gasp" means he just wanted to let out a gasp, not that he did actually let out a gasp?
Best Answer
I think it's a form of the imperfect in English. The modal "would" is the past tense of "will", but, as a past tense, it often functions as the English equivalent of the imperfect tense, which has its own inflectional form in many Romance languages. In this instance, I think it is the past tense of "will" and it's acting as an imperfect. In essence, it is trying to convey the notion that whenever someone is elbowed in the ribs, it will usually knock the wind out of him or cause him to gasp for air. In this instance, when Harry was elbowed in the ribs, he would let out the customary audible gasp.
J.K. Rowling did not have to use the past tense of "will" (would) here; she could have just said, "He let out an audible gasp," and it would have been fine. I think she just used the past tense of "will" for style here.
That's the best I can do to help you out here. I know her use of "would" here sounds fine to my native ears and there's nothing wrong with Rowling's grammar in this sentence; it's just her style coming out in the ink in my mind.