The person in question is your son. Think about it this way: Who is "your father's son"? It's you, because you have no brothers or sisters. So, you just replace "your father's son" with "you", and the riddle now reads: "...that man's father is you." Simple.
Man's father = My father's son. My father's son = me. That man's father = me. I am the father of my son.
Nephew
Either your son or your nephew is the man.Your father's son is either you or your brother (including half-brother).If your father's son is you, then the original man is your son, (you are his father).If your father's son is your brother, then the original man is your nephew, (your brother is his father).Obviously if you have no brothers, than it must be your son.
An intoxicated man at a party
My son. "My fathers son" is myself, if I don't have brothers and sisters.Therefore, "A certain man's father is my father's son" simplifies to "A certain man's father is myself".
The person in question is your son. Think about it this way: Who is "your father's son"? It's you, because you have no brothers or sisters. So, you just replace "your father's son" with "you", and the riddle now reads: "...that man's father is you." Simple.
That means that the man in the photo is his son. "My father's son" is himself (since he has no brothers and sisters); since he is the father of "that man", it follows that "that man" is his son.
his son
His son.
his brother
you/me
There are only three people: a grandfather, father, and son. The grandfather is the father of the father, the father is the son of the grandfather, and the son is the son of the father. That's why two fathers and sons who each caught one fish brought three home.
The father's son is the uncle of the son of the father's daughter.
your grandfather is the relative which is described - a) (If I am a female) your grandfather is my father's son, therefore I am your grandaunt (your grandfather is my brother) - b) (If I am a male) your grandfather is my father's son, therefore I am your granduncle (your grandfather is my brother) - c) (but if I am a sole son/daughter) I am your grandfather/grandmother
The usual way this puzzle is stated is... A man is showing a photograph of a man to a friend of his. He says Uncles and brothers have I none, But this man's father is my father's son. Who is the person in the picture? The picture is of his son.
He is your grandson. If his father is your son, he is your grandson.