responding to Tweedledee A full decision tree enumerating all events that might happen is presented in the Grinstead and Snell book an elementary probability textbook in the articles references available online  Although presented there as a decision tree this tree is for all intents and purposes the same thing as a sample space  A similar tree from both Carlton and Chun also in the references showing only the events following player initially picks door  is presented in the article in the Conditional probability by direct calculation section  If youre having trouble understanding the text in this section or simply think its unclear its fair to ask here for the text to be clarified  I hope you dont take offense but it seems like youre having trouble understanding the basic concepts of sample spaces and how they change in response to events  This sort of discussion belongs on the Arguments subpage as this article is not a tutorial on basic probability theory  And perhaps a more direct response the article does not mention sample spaces because thats not how most references approach the problem