or consider this approach: when you nominate a door you split the objects into His and Mine. He has two and you have one, so he probably has the car ('probably' here meaning 'more likely than not'). Now he shows you a goat - you always knew that he had at least one, so you have learned nothing and therefore still think he probably has the car. The only difference now is that you know WHERE the car is if he has it. So you argue: he probably has the car, and he certainly would put it THERE..... so it probably is THERE. Clearly you must change your choice.