Webster defines a fact as “something that has actual existence”. It defines existence as “the state or fact of having being especially independently of human consciousness and as contrasted with nonexistence.” Therein lies the circular difficulty of the concept. A fact is defined by, and limited to, our perceptions and our knowledge base, which is never constant. That which we “knew” to be fact 30 years ago may be suspect today. That which we know today may be thrown over by the discoveries of tomorrow.
Science is a tool that helps us explore, define and understand the “facts” of our world. What we hold as scientific fact is constantly in flux, changing as we delve deeper and deeper into our incredibly complex universe. We have probably just barely scraped the surface. How can we arrogantly say that what we know now is fact, absolute truth? Certain philosophers believe there is no such thing as absolute truth. Philosophy is a game of concepts and ideas that can use reason to prove anything to be “true”, or it can lead you into a merry circular mind trap you may never escape from. It has it’s purpose in the world, but finding fact is not it.
So Webster, science, and philosophy cannot even tell us with absolute certainty “What is fact”. What do we do? That is up to each and every one of us to decide. We all start out with a system of “beliefs” given to us by our family, and our environment. It up to us to question and evaluate said system to either truly make it our own, or to move on to one that better suits our own perception of fact. Not a very stable answer, is it?