Our entire world is a construct of the brain as interpreted through signals received from the sensory organs. There is no such thing as "bright" or "hot" or even "color" except in subjective experience, so why couldn't this be true of everything else too?
Many philosophers and epistemologists agree that reaching "absolute certainty" in terms of our knowledge of anything is impossible. We can't even be absolutely certain of our own existence (we could be in the matrix or a brain in a vat). We can, however, be MAXIMALLY certain.
Beyond all reasonable doubt should be as good as certain.
I will not know for certain that tomorrow I might be showered in cow sized golden frogs made of uranium, however I know beyond all reasonable doubt that I will not experience such an event.
certainty is determined by reality, which is determined by concentration and knowledge of each individual, thus, we can know something for certain if we establish the term "certainty" as a fact that is temporary provable, but also discredited.
We can get more benefit from some theory or idea than from the other, which may suggest that we are on the right path to getting closer to the truth, adopting that point of view and not the other.
Human fallacy does not prove you cannot know anything for certain. For instance, humans could create an artificial intelligence without these imperfections. If they did so, this conjecture still applies to them with equal validity.
gappleto97
Some things can be proved and therefore known for certain; water is wet, the sky is blue, gravity is in effect, you cannot destroy or create energy, merely convert it. Etc.