Read Devlin's column again. A B and C are used by Devlin as follows. A is the door that the contestant chooses, C is the "wrong" door that Monty opens and B is the other door that "was not opened". You are arguing apples instead of oranges because using Devlin's lingo, door B is never the door opened by Monty. You must use Devlin's lingo if you are to argue an error in his logic. You did not. You are right only if you do not follow the lingo in Devlin's column, but that does'nt mean that Devlin's column was wrong. The probability that the car is behind door B (using Devlin's lingo) is truely 2 in 3 because it can't be behind door C which is a wrong door "The car is not behind door C".