Ch 8: General Claims

What I found very interesting and helpful in Chapter 8 was how to reason with general claims. According to Epstein, “general claims are how we assert something about all or part of a collection.” Epstein talks about the different ways on how to use the words, “all, some, no, and only” when making an argument. Sometimes there are arguments in which they may seem valid to us but they’re actually not. The premises could be true but the conclusion may be false. Here is an example:

All guys who go to the gym want to build a six pack. John goes to the gym. So John wants to build a six pack.

The example above may seem valid but it’s actually invalid. If John goes to the gym, it does not mean that he wants to build a six pack; he may want to lose some pounds or even go check out some girls. There are many other possibilities so the conclusion may not be true. To prevent ourselves from getting lured into believing in these kind of arguments, we need to understand the difference between “all” and “some”.
According to the text, “all” means “Every single one, no exceptions” and “some” means “at least one”.
There are actually many equivalent ways to say “all” and “some“. For example,:

All witches are evil = Witches are evil
Some guys are strong = At least one guy is strong