When Yosef dreams that the sun, moon, and eleven stars will bow down to him, Yaakov expresses dismay or disbelief that the whole family is destined to serve Yosef:
"מה החלום הזה אשר חלמת, הבוא נבוא אני ואמך ואחיך להשתחות לך ארצה?"
The obvious problem with the dream, and with Yaakov's interpretation of it, is that such a scenario is impossible. Yosef's mother (Rachel) is already dead, so she won't ever be able to bow down to Yosef. Shouldn't this be clear to everyone?
We must conclude that the question is rhetorical, and that Yaakov meant to point out the impossibility of the dream's fulfillment, given Rachel's death. Interestingly, Yaakov's statement may explicitly hint at this. A sequence of six letters in the middle of the statement spells out the Hebrew for "Rachel is dead":
"...אשר חלמת הבא..."
This could be a great example of the idea that every letter in the Torah has meaning. But even if unintentional, it would still be a pretty cool coincidence. Credit goes to R' Amnon Bazak for pointing out this "subliminal message".
By the way, I heard it suggested that the sun and moon actually represent Egypt and Mesopotamia, the two main civilizations of the time, which were subservient to Yosef at the time of the famine. This, of course, would make the dream much more ambitious that one might have thought. And of course, there is always Chazal's interpretation that the sun was indeed Yaakov, but that the moon was meaningless, because all dreams include an element of nonsense.
