Valid and Invalid

Valid and invalid arguments were hard to understand but reading the examples helped me a lot with understanding. Invalid and valid arguments use words like: all, some, or no.  These words are used to reason valid arguments. 

There were many ways of doing so.  The two I will be discussing is:

 - The direct way of reasoning with all

The valid argument goes like this:

 All dogs bark. Poochie is a dog. So Larry barks.

The invalid argument goes like this:

 All dogs bark. Poochie barks. So Poochie is a dog.

Chapter 8 of Epstein uses diagrams to prove the validity of the arguments.  To check the validity means to make sure the parts of the diagram over lap and draws a picture that gets the point across to the person trying to understand the argument.

The following image would be what an argument diagram that would be used to check the validity.

http://www.thinkingshop.com/Clarion/logic/images/AProp-4-6.jpg