yevamos 90 הוראת שעה

the gemara tries to prove that the sages have power to go against the torah from the story of אליהו בהר הכרמל. Tosfos asks (here and in tosfos yeshanim and in sanhedrin), how can we bring a proof from אליהו if he did it ע"פ הדיבור, one track of tosfos is to say that if not that חכמים have a power to go against the torah then נבואה wouldn't help since אין נביא רשאי לחדש דבר.
Another track of tosfos holds that no, and there is in fact a concept of הוראת שעה ע"פ הדיבור. This also seems to be the opinion of the rambam.

Interesting that we find this concept of הוראת שעה mentioned all over shas (my search brought up 18 places, but some sugyas mentioned it more then once in the same context). so according to the opinion that holds there no such power as to against the torah ע"פ נבואה all these places will have to be למיגדר מילתא.

To end with a note of Machsava, Rav Hutner has a piece (i think its in rosh hashansa) that shows that all the beginnings were הוראת שעה. The kurbanos of the מילואים and the same by the 1st bais hamikdash were all diferent then the norm. in the 2nd bais hamikdash, it was the miracle of chanuka that fulfiled this concept. with this he explains the psukim in יחזקאל regarding the 3rd bais hamikdash. a fascinating must see piece.

the depth here is what the rambam really says in the מורה and that is that the rule for sustaining the thing is the opposite of its point of creation. for example, he says there that if a child was born in an island stranded there with only men, the men can teach the child to read etc so that one day when they reach civilization he will be able to fit in. But one thing the child cannot comprehend- the birth of a child. if you were to tell this child that a man is created in an enviorment where he is immersed in water and his lungs are collapsed and no food enters his mouth etc. he will think you are mad! Hashem created nature this way to teach us that although this world follows the rules of nature and exists within a framework of time and place, but the point of origin is exactly the opposite.

and it MUST be that way, because to be created has to come from outside the system. too long for a blog...