Flaws in Logical Reasoning

[Adeline]

Hi!

As I do more flawed LR questions, I am a little confused about the difference between "overgeneralization" and the "error in the use of evidence" (specifically using some evidence for a position to prove that position is true).

I don't have a specific question to refer to for this post, but when I was doing the drill, I found myself hesitated when I saw questions that use some evidence or one single evidence to make a conclusion that something exists/is true. It seems to me that "overgeneralization" and "error in the use of evidence" can both describe this flaw.

I wonder is there a way to distinguish these two types of flaws? Or that it doesn't matter how to classify this flaw of reasoning in a certain category as long as I can identify what the error is?

Thank you!

[Adam Tyson]

Hey Adeline, an overgeneralization is a type of evidence error. There are many types of evidence errors for which we have handy names, like a "lack of evidence error" (using a lack of evidence for a position to prove the opposite position is correct), a "some evidence error" (treating evidence that weakens an argument as if it destroys the argument, or evidence that strengthens an argument as if it proves the conclusion), a general lack of relevant evidence (the evidence offered doesn't address the issue being argued), an exceptional case error (where evidence of an outlier or exception to a general rule is treated as if it is representative of the norm rather than an exception; this can also be called an overgeneralization), and errors of composition and division (part-to-whole and whole-to-part flaws).

Sometimes, we can see that an argument uses evidence in a way that isn't valid, but we cannot quite put a name on it from that list. Recent LSATs have had more and more flaws that are hard to name using the standard descriptions that we cover in our materials. They are, as my colleague Jon says, "slippery" in their language, hard to get a firm grip on and label with ease. When that happens, we have to let go of the idea that we have to name the flaw, and instead we need to just describe it in our own words. Sometimes you can't quite name it or define it exactly, but you know it has to do with an improper use of evidence, and you can just say "that's an evidence error of some kind, and I am not going to worry about the exact label to put on it." It's like a certain famous legal decision that you may have heard about, where the Court said about pornography, "I know it when I see it."

When you can name the flaw based on the things you have studied, that's great! It will help you zero in on the correct answer quickly and easily. When you cannot, then you need to use your own words to prephrase a description of the flaw, and then eliminate the answer choices that describe some other flaw, or that do not describe a flaw at all. What you are left with should be the correct answer!

[Adeline]

Hi Adam,
Thank you for your thorough explanation. I am clear about this issue now!
I really appreciate it

[medialaw111516]

For flaw/weaken questions that are talking about surveys, is it reasonable to say that we are usually looking at a sampling error? In my course, we discussed that the mere mention of surveys in LR should put is on guard for a potential flaw question stem coming up, so I'm wondering if that's because sampling issues are common.

[Dave Killoran]

Hi Media,

Sampling errors certainly come up, although there are other issues too with surveys such as having the questions improperly constructed or having people lie about their responses. We talked about this in some detail on our podcast, in Episode 26 at http://www.powerscore.com/lsat/podcast/, at the 49:00 minute mark. I think that would help shed some extra light on your specific question here

thanks!