Indeed. Unfortunately the assumption that your logical framework always holds in the real world may not be valid. [/b]
Undoubtedly. However, until we are shown that what our logical framework holds to be real is in fact not, then we can only stick to what our logical framework tells us, at which point we can begin to modify our understanding of other things. Personally, when writing a paper for school, I find it far easier to assume what I know to be real(that is, am pretty sure I know to be real, having not yet been shown different) is in fact real (rather, has been displayed up to this point to be real) then writing countless side notes (more accurately, what my mind has come to describe as side notes) indicating that each point, law, etc. is only believed ot be valid, but may not be (at least, valid as we have come to define it). Do you see what I have just displayed? What I'm trying to say is, until we are shown different, we'll have to trust what we've been shown is valid.
To remotely tie this into aikido, umm... it's safe to assume that when you throw uke, uke will hit the mat due to gravity rather than fly out of orbit, because of the laws of gravity we have come to believe as valid have yet to be disproved or altered.