In a topic about
negative structure: negative question, Swan said that a question could ask a confirmation of a negative belief. So, let's look at the following two sentences:
Oh, Dear. Can't they come this evening?
Oh, Dear. Couldn't they come this evening?
The first sentence was provided by Swan, but the second is mine. As far as I understand what Swan said, the first sentence shows the speaker suspects that they didn't come. In contrast, in the second sentence, the speaker shows that it might be good if they come.
Am I correct?