Right, but he says THAT MAN'S FATHER is my father's son, therefore that man's father is him, and so that man must be his son.

I agree. My son is the answer.

No it's not.
The answer was "He is the father."

Well, if you had actually presented a question, such as What was he in relation to the dead man, that would be the right answer. Since you didn't though, saying the dead man was his son is correct in that it comes to the general conclusion that the riddle wants you to get at.

Ha it didn't say THAT in the instruction book, clever cardboard...Slow Lexxingggtonn...Time for a new riddle?

"Brothers and sisters I have none, that man's father is my father's son."

Break it down with logic...is my fathers son (remember he has no brothers or sisters) so he refers to himself + is that mans father = his son.

You guys aren't going to stop now are you?

Leaving the community with naught but an old answer and no question.

How much wood would a woodchuck chuck if a woodchuck could chuck wood?

:(

37... the answer is always 37...