Then, doing your reading again, you find that the paradigms of your people are about to change during the next decade. Assume that the method to interpret the Holy Scripture will change, or the way to visualize the human body. No, reality did not enter into any of the arguments above at all. You take note what from now on, with the new paradigms accepted, must not or can happen in your campaign, and that could be it. But it probably won't.
Paradigm shifts are marvelous campaign devices.
They can, but need not, be connected to a change of an underlying reality. You might find out, too, that by storytelling these paradigm shifts, and thereby looking at many facets of them, you get a better grasp on medieval world views yourself. A cathedral might be read quite differently if you can crossreference its sculptures and architecture to the examples of paradigm shifts given above. They serve to describe the relations among scientific communities, not the 'reality'. If a storyteller has to decide about something in the game, she can use dice, rule books, common sense, player psychology, paradigms and, last, her concept of medieval 'reality'.