||This web of influence has
interesting ramifications from the perspective of the types of reasoning
patterns that it supports. Consider
Forrest Gump. A priori, we believe
that he is pretty likely to be smart.
Evidence about two classes that he took changes our probabilities only
very slightly. However, we see that
most people who took CS101 got A’s. In
fact, even people who did fairly poorly in other classes got an A in
CS101. Therefore, we believe that
CS101 is probably an easy class. To
get a C in an easy class is unlikely for a smart student, so our probability
that Forrest Gump is smart goes down substantially.