How do we know anything? We might be able to say that we know something because of a justification, but that justification also needs to be justified by a justification to even be a justification. Every justification needs its own justification, either to infinity (good luck with getting infinite justifications), or until the justifications are circular. Without using circular reasoning, it's infeasible for you to know anything, even whether or not circular reasoning is valid. So, how do I know anything? Simple, I know God lets me know through science and observation and God lets me know that he lets me know. I am justified in believing this is true because it must be true because it is true; it is true therefore it is true. If there's something wrong with circular reasoning, prove it or you don't know that. Good luck doing that if circular reasoning and assumptions are invalid in proving things.