Chapter 3, Tutorial 3
Informal Fallacies  

There are many things that can go wrong with informal thinking. If, for example, I've often heard from various people riding the bus that our current president is courageous, is that good reason for thinking it true? It's difficult to tell. We don't typically know the people we ride with on a bus, and it's hard to know how much weight to put on their opinion. Still, we do trust people generally. The best we can do when assessing informal thinking is to be critical with respect to the evidence cited for conclusions.