2. Melvin Chapman existed.

Melvin Chapman existed. He was a real person. He was my grandfather. I know this because I know people who knew him. There is a lineage of reliable sources-- in fact, there are multiple reliable lineages, because I know many people who knew him personally. All of these people agree that he existed, and have many stories and characterizations that agree and corroborate one another. I know that none of them are mentally disabled or insane, and on the whole their memories are quite good. Also corroborating the memories are census records-- the names and ages and locations match with stories that I have been told. Thus, I believe in his existence although I have no memories of my own to attest to that. Melvin Chapman lived.

Objectively, I cannot prove this. It relies on the assumption that I myself am a reliable source to be trusted. I would like to believe that I am, but a skeptic would not take that at face value. As such, we have reached an impasse.