On Wikipedia, knowledge is defined as justified true belief:
The concept of justified true belief states that in order to know that a given proposition is true, one must not only believe the relevant true proposition, but also have justification for doing so. In more formal terms, an agent S knows that a proposition P is true if and only if:
- P is true
- S believes that P is true, and
- S is justified in believing that P is true
So can we really know something if we cannot know whether it is true? For example, if I know dinosaurs did exist once, then:
- Dinosaurs did exist once
- I believe dinosaurs did exist once
- I'm justified in believing that dinosaurs did exist once
The last two are satisfied: I do believe dinosaurs did exist once, and I'm justified in believing that, by what I know through biology and archaeology (ancient, large bones that match the shapes of giant weird animals). It is very strong evidence, but I still not know whether or not dinosaurs did exist once.
Now, I know not all truths are established truths. From The Analysis of Knowledge (Stanford Encyclopedia of Philosophy):
Something’s truth does not require that anyone can know or prove that it is true. Not all truths are established truths. If you flip a coin and never check how it landed, it may be true that it landed heads, even if nobody has any way to tell. Truth is a metaphysical, as opposed to epistemological, notion: truth is a matter of how things are, not how they can be shown to be.
So it seems that for anything that we cannot directly check its truth but only infer it, we can only have justified belief on it. But then, the statement "Dinosaurs did exist once" is commonly regarded as "knowledge". So is this statement actual knowledge, or is it just justified belief?