Thanks...
I see..
Then, understanding it as a past tense subjunctive referring to the present, like, "You could be right.", meaning "There should be one time that you
do not get it." is impossible?
Watching dramas or movies in English, when a friend tries to give a high-price gift, then her friend says, “I couldn’t take” or “I couldn’t”.
Also, “Could you be more queer?” is meaning that the listener is(not was) very queer….
Here, in these two cases, “could” definitely is referring to the present situation, so it is understood as a subjunctive, not simple indicative.
Therefore, I assumed this paragraph from Harry Potter could also be a subjunctive……