Examples of Unknown and Unknowable Truths
Sometimes people say that for logical reasons there can be no examples of unknown or unknowable truths. The logical reason is this: to know that p is an unknown truth requires knowing that p is true, which contradicts the requirement of p being unknown.
Before I give examples of unknown and unknowable truths let me give examples of philosophers who died more than 100 years ago: Hume, Leibniz, Kant, and the philosopher first born in the 16th century. One might have thought that it is impossible for physical reasons to give such examples. After all, a philosopher who died more than 100 years ago just isn't there any more, so he can't be given as an example. But not so. In order to give an example of a dead philosopher it suffices to name or describe one; it is not necessary to dig him out.
Why should it be different with truths? To give an example of an unknown truth it suffices to name or describe one. And that's easy. For example, I forgot what I dreamt last night. Let D be a correct description of my dream(s). D is an unknown truth. Another example: One the following sentences is (or expresses) an unknown truth:
The number of coins in my pocket is even.
It is not the case that the number of coins in my pocket is even.
If you think it matters I can even tell you which of them is the unknown truth: the true one.
Question: would it be appropriate to offer "I am not a brain in a vat" as an unknown truth? I believe it is true, and I believe it can be reasonably classified as unknown. So it should count. The problem is that perhaps the present context is one of those contexts where "knowledge" means "true belief".
What about unknowable truths? Well, if p is an unknown truth, then the conjunction of p and 'p is unknown' is an unknowable truth. So for each example of an unknown truth, we get an unknowable truth for free. Another example: Let F be the complete description of all fundamental facts in our world (on my view, complete microphysics), together with the statement that these are all the fundamental facts. F is certainly unknown; but it is also unknowable. For in order to be known it must be true (unless in the present context "knowledge" means "belief"). And in worlds where there are more intelligent creatures than hereabout, F is false.