General Claims in Chapter 8

In Chapter 8, section A we learned how to reason using general claims about something in general way so that it applies to all or part of its claims. In further detail, we learned of how to make the claim in more than one way. The author used an example that I find was really helpful in making it clear to understand:

“Only postal employees deliver U.S. mail.

Ralph is a postal employee.

So Ralph delivers U.S. mail.”

The general definition of Only is “Only A are B” means “All B are A.” not all A are B. By glancing at the referred claim, one would assume that it sounds valid but this is actually not a valid claim. This is stating that only postal employees deliver U.S. mail but that does not mean all postal employees deliver U.S. mail so Ralph may not deliver mail therefore making this claim not valid.