I'm an academic sceptic so we start with knowing nothing at all. Nothing is certain ('haha', except the philosophy that nothing is certain, I'm not falling for that one). Empirical knowledge is unreliable and inductive theories control the world.
For an academic sceptic nothing is certain and he will only accept a theorie for true if it is most likely to be true. In our world this is fact. There's a theory, let's say the atommodel, and it holds until somebody else comes up with a new, better, more probable theory about it, throwing out the old theory.
When you look closely at our knowledge, everything was built up this way. Decartes said it, I know nothing for sure but since I can doubt myself I have to exist (yes, cogito ergo sum :)).
I'm gonna leave it at this for now. I want to do this step by step and I still have to figure out what the best and most logical steps are to do this...