Shalom,
What is the point of such a kasha: a man falling off a roof and having relations b'shogeg. This is impossible, no?
Awaiting the Rav's reply.
Feldman
Dear Feldman,
Tosfos Kesuvos 4b DH Ad explains that we find the Gemara discusses subjects that don't normally happen or even will never happen - the reason is Derosh v'Kabel Sachar - learn and receive reward. What the Torah wants in a hypothetical case is part of Hash-m's Torah.
Other examples given are: using a live animal for the wall of a coffin (Kesuvos 4b according to Rashi) and in Chulin 70a we find, "What if a weasel enters the womb of a pregnant cow, swallows the embryo, leaves the womb, then returns inside and returns the embryo, then when birth occurs is the calf considered a first born?"
All the best,
Reuven Weiner