If I say that tomorrow will be fine, what does this enunciation mean? Perhaps it means that it ought to be fine, if the glass tells truly; then it is the inference of a probability. Perhaps it means no more than a surmise, because it is fine today, or has been so for the week past. And perhaps it is a compliance with the word of another, in which case it is sometimes a real assent, sometimes a polite assertion or a wish. (Grammar, Pt. I, Ch. 4)Here is the other quote:
“Good Morning!" said Bilbo, and he meant it. The sun was shining, and the grass was very green. But Gandalf looked at him from under long bushy eyebrows that stuck out further than the brim of his shady hat.Of course, for Bilbo, it is a real assertion, not just a "profession," which is what Newman is talking about.
"What do you mean?" he said. "Do you wish me a good morning, or mean that it is a good morning whether I want it or not; or that you feel good this morning; or that it is a morning to be good on?"
"All of them at once," said Bilbo. "And a very fine morning for a pipe of tobacco out of doors, into the bargain.
"Good morning!" he said at last. "We don't want any adventures here, thank you! You might try over The Hill or across The Water." By this he meant that the conversation was at an end.
"What a lot of things you do use Good morning for!" said Gandalf. "Now you mean that you want to get rid of me, and that it won't be good till I move off.” J.R.R. Tolkien, The Hobbit, "The Unexpected Party."