If the PM enjoys the confidence of the House of Commons, then the Governor-General must do his or her bidding. On Thursday December 4th, Prime Minister Stephen Harper asked the GG to prorogue Parliament so that he would not have to face the House on a vote of confidence. Should she have acceded to his request? If he had the confidence of the House, she was obliged to do so. If he did not, she was obliged not to do so.
Here's a problem in what I call constitutional epistemology. Does the GG know that Harper did not have the confidence of the House? Well, in the ordinary sense, yes. Nobody could doubt that a majority of members of the House had no confidence in him. They said so. They signed pieces of paper to that effect.
Nevertheless, they had voted to receive the Speech from the Throne. So when the Commons had voted last in a confidence measure, they demonstrated confidence in Harper's government. Thus, the GG does not know, in a constitutional sense, that he does not have the confidence of the House.
I love tidy reasoning like that. Nice.