Question

How can we be CERTAIN we know anything at all?

Answer 1

• We can know everything there is to know at a level of utmost certainty within a given context. Knowledge is contextual. And unless specifically categorized otherwise, content of knowledge is always certain, its always definite.
• We can know stuff for certain, and there can be unequivocal answers to certain questions. That's what logic and mathematics are for: when you 'prove' something in mathematics, you're demonstrating that given certain assumptions, another proposition must be true. If the assumptions are true, the conclusion is too, and we can know that 'for certain.' It's a timeless, eternal truth, unless you made a mistake in your proof.
• This is because our knowledge is inductive: we don't know everything, so our ideas and understanding are based on what we know.It is the correspondence between your worldviews and ideas with the world that gives you reinforcement and less uncertainty.
• Our understanding of the universe has thus been ever been more firm, thanks to great discoveries and well-fitting theories that are tested (and rejected) through ever improving methods, called science.