Logical Reasoning Questions Answered: What are Mistaken Reversals and Mistaken Negations?

what-s-that-1527433Lucy K. reached out to me with some questions about Logical Reasoning and asking for resources on mistaken reversals and mistaken negations. Here's what I told her about these terms and whether they're important when studying for the LSAT. Lucy K.: I'm working on a review of conditional reasoning right now. Do you have any resources on mistaken reversals? And also mistaken negations? I just worked through the LRB chapters on Weaken and Must Be True questions. The Weaken practice problem set went better than the Must Be True problem set, but I want to review them both. Right now I've been noticing that Weaken questions, compare/contrast dialogue between two speakers, // reasoning, principle, sufficient assumption, and flaw questions are LRs I've tended to get wrong.

I've noticed that I tend to get weirded out by long arguments, arguments with lots of formal logic, and some of the science/nature arguments (I always think I don't know what this jargon-word means, or I'm not an architect, biologist, anthropologist, et cetera, what if I'm missing something about a scientific process, or I think it would be great to diagram this LR question as I see the logic words, but I'm really scared that I'd diagram it wrong and/or am debating which abbreviations to use). I would like to practice these more.

Nathan: Oh dear. "Mistaken reversals"... "mistaken negations"... they're one and the same. I'm sorry you even have those two terms in your head, because you really don't need them. This is just something that LSAT dorks say when they want to impress someone. Logically, it's the exact same flaw. All you really need is the big picture. One example should suffice.

Premise: If you're eaten by a shark, then you're dead.

Mistaken reversal: Everyone who's dead was eaten by a shark. This is stupid because there are a lot of other ways to die. Like maybe a flock of rabid turkeys pecks you to death. Or whatever. Point is, it's obviously stupid. And believe it or not, this simple, obvious flaw is the LSAT's favorite thing to test. It's on every single LSAT.

Mistaken negation: If you're not eaten by a shark, then you're not dead. See, that's a slightly different statement but it's logically identical and it's stupid for the exact same reason. What about the rabid turkeys? What about all the other ways to die? This, again, is the LSAT's most common flaw.

Formally, the two flaws are contrapositives of one another. I suppose there is a technical difference in the form of the flaw, but it's simply not important enough of a distinction for you to bother knowing two different names for them. The terms "mistaken reversal" and "mistaken negation" have never appeared on the LSAT. Only in LSAT books. But not in my LSAT books, because I don't want you to waste your time on irrelevant technicalities.Generally, I am not in love with Powerscore's Logical Reasoning Bible for exactly this reason. It focuses on too many trees, so unsuspecting readers often miss the forest. It's not technically wrong (at least not often) but it's far too technical. Students come away thinking that the LSAT is harder than it really is.

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