Well, you can always take the teenage philosopher's view of ignoring anything you don't like and justifying it by saying that nobody really "knows" anything. Man. But in productive scientific or grownup conversation, agreed upon observations could be thought of as facts.
Observable phenomena are facts, starting points or perhaps premises is a good word. But they're 'things which happened' that you can have competing explanations
for. Successful theories can also be referred to as facts: it's always been an observable phenomena that things fall down, but with so many experiments explained just by "
massive things attract other massive things", it would be perfectly cromulent to describe that attraction itself as a fact and on the whole keep discussions aimed at the (still very mysterious)
mechanism of action for that attraction.