I was recently given the following question in an exam.
Determine the soundness of the following argument:
John lives on the same street as Mary.
Mary lives on the same street as Sam.
Therefore, Sam lives on the same street as John.
I understand that an argument is sound when it is valid and all the premises are in fact true.
The problem with the above argument is that I have no way of knowing whether or not the premises are in fact true. I don't know for a fact on which street Mary, John and Sam live. I don't even know who they are.
Looking through past exam papers it seems to be a common trend for the examiner to ask whether or not arguments with premises like these are sound or not.
What is the correct way to determine the soundness of arguments where the truthfulness of the premises fall outside of our range of knowledge?