This matter about epistemology was resolved many years ago in different ways by both Karl Popper and Thomas Kuhn.
Karl Popper describes intersubjectivity, meaning that everything you describe is a kind of consensus you establish with the people you are talking with in first place. Homonyms are an example of this: if you're talking regarding police officers and you use the word dick, there is a chance you're talking about a detective rather than about a penis.
Aside from the definitions, there is intersubjectivity in the propositions: We all can see the sun rises everyday, and never discuss that fact. But that intersubjectivity is nothing more than our assertion of the reality (this becomes more common when you assert something about people's behaviour depending on what you're used to see). This plays a significant role in fact sciences when we have to describe what elements are in play (forces, masses, energy, ...) and we all agree the existence of such concepts, their meanings, and how do we perceive them.
Kuhn goes even further: He describes the crude reality that the way you describe your world may not be intersubjective at all, coining the term of paradigm, which has a set of core values/beliefs as its starting element. It doesn't mean that -forcefully- it won't, but there is a high chance that it might occur. Examples of that:
- Is light a wave or a particle? regarding early quantum mechanics.
- Is an embryo a person or not? regarding the currently active debate of abortion right now in Argentina.
The saddest part is that Kuhn describes the interaction of different paradigms more like a darwinian struggle than an actual evolution of knowledge, on which you just get convinced or stay in your paradigm (however, when he writes an addendum regarding others philosophers calling him irrationalist or relativist, he argues than such struggle heads always towards an evolution of sciences with more precise knowledge).
So the answer is yes and no regarding the existence of facts:
- Yes: We can say that, for people watching the same, the facts do exist. They will perceive something... moving. Perhaps. Unless somehow they don't, and that is just a person's sensorial mistake, say.
- No: Depicting facts is more about language, semantics, and a core set of starting values than about what actually happened. A perception may be interpreted and described in potentially infinite number of ways, and so creating different propositions (a fact is just a primitive proposition - even Prolog uses that concept in this way).
The point here is that facts are propositions, and are an abstraction of what we pick with our senses (they abstract the energy and surroundings we can perceive) and what we describe with our core values and our languages (which are abstractions of the stimuli provided by our senses).
There is something that is stated in Fides et Ratio which, believer or not, you should take as starting point if you defend the facts: You are defending the path of obeying your direct (or indirect) senses. This is important: There are sciences having an object of study which is not related to our senses. One of them is theology, which studies what is written in the Bible (regardless the actual truth of what is described there as things that actually happened or not). Formal sciences also fit here (math, logic). Finally, when you study laws everything gets more complicated (as an introductory subject, they tend to discuss whether it is a science, it is not, or it has a scientific component aside to other types of components). So you must remember which one is your starting point, object of study, or core set of values before even starting to debate. You cannot prove anything, in your corrent system, which is beyond your starting point (thanks, Gödel).
My tip to you: Don't go that way. There is no way you can prove or disprove anything going the way of the solipsism. Either you find a starting point you both share, or every discussion will be pointless.
And Rivière's corpse is opening a Chandon while we discuss this topic.