[TheCount212]

Use logic to determine (1) what opponent has (2) what opponent thinks you have and (3) what opponent thinks you think he has. This assumes that the opponent acts rationally and plays well, because you have to trace back through his decisions to determine what he would do if he held xx PF, flop, turn, and river. If the opponent plays poorly or acts irrationally it becomes nearly impossible to put him on a hand unless you have played with him many times and pick up on betting patterns or tells.