The purpose of including #2 in this lesson is to make you aware that there is the possibility for false premises on the LSAT. While the vast majority of the time you should assume that the premises presented to you are true, there are the occasional premises on the LSAT that will be glaringly false, and the identification of a false premise is one way to invalidate an argument.
In this example, the premise that anyone named Sue is a girl is proven to be false. This is evidenced by the song "A Boy Named Sue." If a boy can be named Sue and X is named Sue, it does not logically follow that X is a girl because X could also be a boy. Therefore, the conclusion of the argument is invalidated because one of the premises used to reach this conclusion has been proven to be false.
For the most part, the premises presented to you throughout your LSAT prep and on the actual test will be true. This example is just included so that you keep in the back of your mind while approaching questions that there is the possibility for false premises to be presented in passages.
Hope this is helpful! Please let us know if you have any further questions.
