Week 6 - 1 of 3

The one thing that I found most useful in chapter 8 section B "Some Valid and Invalid Forms". I am going to focus on direct reasoning and arguing backwards with "all". When reasoning directly, the arguments are true. For instance, All humans have belly buttons. Sarah has a belly button. So Sarah is human. This example shows that if All S are P; a is S; So a is P. Which is valid. When arguing backwards with "all" the argument is usually weak. Here is an example: All gymnasts are left handed. Jill is left handed. So Jill is a gymnast. This argument is weak because it does not include all the possibilities. Jill can be a swimmer, a soccer player, and/or not do gymnastics at all. So this example shows that All S are P; a is P; so a is S. These two example show the difference between a valid argument and a weak one. Using the direct way of reasoning is more accurate and easier to come across a valid argument than to argue backwards.