Final answer:
The riddle involves three generations: a grandfather, his son, and his grandson, accounting for two fathers and two sons and bringing home three fish.
Step-by-step explanation:
The question regarding the two fathers and two sons catching fish but bringing home only three fish is a classic example of a riddle. This situation can be logically explained without anyone throwing back a fish, sharing, or selecting only the largest fish. The answer is that there are actually only three people fishing because they represent three generations: a grandfather, his son (who is also a father to the grandson), and the grandson (who is the son).
Therefore, there are two fathers (the grandfather and his son) and two sons (the son and the grandson), but only three people. Hence, no other actions like throwing a fish back or not fishing are necessary to account for the three caught fish.