We rely on axioms to do anything.
We presuppose we are rational.
We presuppose our senses are not deceiving us.
We presuppose we can view the external world.
Under these presuppositions we can lets say speculate on the world but that doesn't mean we know things. It just means under specific axioms we can speculate on the external world. If we did know something we wouldn't be using axioms instead we use it because it is the only way to observe what is around but that doesn't mean we know.
This is mainly used for people to counter what I said or give examples of when we have known something.
Hopefully you understand what I am trying to say.