FM, I don't know where you studied Philosophy but Epistemology is the science of "how" we know something and the problem was solved a long time ago by a man named Aristotle. It is the evidence of the senses.
Below is a link that gives a brief description of the Objectivist Philosophy to include Epistemology and what it means.


http://www.aynrand.org/site/PageServ...ectivism_intro