I guess it is unproblematic that knowledge can be communicated.
I can know that P because I read that P in some reliable source; or I can know that P because some reliable person told me that P.
I might for example read in some encyclopedia that Luanda is the capital of Angola. I take it that if Luanda is capital of Angola, I did learn something and I now know that Luanda is capital of Angola. Or maybe some friend just returned from Angola, and he tells me that information. Again, I think it is clear that I come to know that Luanda is the capital of Angola.
Now for the complication…
Suppose that my friend which came from Angola doesn’t understand Portuguese. What he was told was in fact that Luanda is the biggest city, and he thought that he has been told that Luanda is the capital. It doesn’t seem right to say that my friend knows that Luanda is the capital of Angola, as his belief is unjustified and based on misunderstanding.
How does this affect my case? I was justified in believing that my friend is telling me a fact about Angola. What he told me is true. So, in some way, I have a justified true belief that Luanda is the capital of Angola.
But surely it is weird to say that I know, and to say that my friend doesn’t know. After all he is the one that told me.
Maybe one should speak about history of justification? Any other ideas?