W9: D3 Ways of reasoning with "All"

A concept from chapter 8 that I found very useful was the use of "all" in arguments.  There is a direct way of reasoning with "all" that will lead to a valid argument, and there is a way of arguing backwards with "all" that will typically lead to a weak argument.

 The direct way of reasoning with "all" follows this structure:

All B are C

T is B

So T is C

An example of this would be:

All babies wear diapers.

Tom is a baby.

So Tom wears diapers.

This leads to a valid argument.

Arguing backwards with "all" leads to generally weak arguments like this:

All babies wear diapers.

Tom wears diapers.

So Tom is a baby.

This is a weak argument because not every single person that wears a diaper is a baby.  This argument is weak because it disregards many other possibilities and therefore it is not a dependable argument.