Student or Learner
Well, I just don't think I can stay now that man has arrived. He frightens me so much, you see. I couldn't possibly act. It could n't possibly be the same, now he's come. And anyway, I ought to go and find my parents.
This sentence is taken from the BNC.
My question is why couldn't rather than can't is used here with the time adverbial of 'now'.
Could I ask native speakers to help me please? Thank you in advance.
"Now" is actually used not to mean "at this point in time", but "since the man came" - "now that man has arrived". The implication is that the man is staying, and the person is thinking about the future of how she (we'll presume it's a woman for now) will be able to act now that the man is there. She is obviously trying to decide what to do in the future ("I ought to go and find my parents.")
So "now" is a red herring. The man came in the past (recently, otherwise "can't" would be more appropriate); and the person is considering her future. She is not talking about how she is acting at this precise moment (now), nor even about she has been able to act since he got there (although this might be relevant to her concerns about the future)
When she says "I couldn't ... " she means "if I stayed". The whole narrative points to the possibilities of the future.
She is trying to make a case for leaving, and part of that is that she "couldn't possibly act the same" if she stayed.