This is only true if the son has had a son of his own.
Man's father = My father's son. My father's son = me. That man's father = me. I am the father of my son.
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.
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.
That man is your brother.
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".
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.
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.
"That man" is the speakers son. However in the original form the final part of the riddle adds "Who am I?" And the answer to THAT question is that "I" is the speaker.
His son.
Himself(2) I think that the question has left out part of the original riddle which goes: "Brothers and sisters have I,none,/But this man's father is my father's son."'My father's son' is me (or my brother or my half-brother or my stepbrother); This man's father is me = I am this man's father = his son;This man's father is my brother = my brother is this man's father = his nephew;This man's father is my half-brother = my half-brother is this man's father = his nephew; This man's father is my stepbrother = my stepbrother is this man's father = no blood relation.If you include 'brothers and sisters have I, none' then the first option is the only valid one , he is looking at a portrait of his son.If the portrait was of himself he would be saying (this man's) = (my) father is my father's son (me or my brother) = I am my own father, or my brother is my father - which would be possible given an incestuous relationship with the mother.The comic song "I'm my own grandpa" plays with this notion and Wikipaedia cites "A proof that a man may be his own Grandfather.-There was a widow and her daughter-in-law, and a man and his son. The widow married the son, and the daughter the old man; the widow was, therefore, mother to her husband's father, consequently grandmother to her own husband. They had a son, to whom she was great-grandmother; now, as the son of a great-grandmother must be either a grandfather or great-uncle, this boy was therefore his own grandfather."
In this particular case "That Man" is my son.
Your father's brother's son's daughter is your second cousin.