BMaker11 on 19 December 2013
that depends on what they're talking about. Things that we have concrete evidence for (evolution, gravity, germ theory, etc) then no, it's not about assumptions. It's about observation and making deductions based on those observations.
We can speculate things, though, but only based on what we can reasonably say is true. For example, we know that atoms are mostly empty space. So if the atoms in the human body were rearranged just a little bit, we could walk through walls.
