Flaws: Mistaken Negation (TM)

PowerScore has trademarked a remarkable number of terms that have become standard LSAT jargon, including the term “Mistaken Negation (TM).” This logical error was identified more than two thousand years before PowerScore trademarked the name, however. Aristotle listed “denying the antecedent” as one of the thirteen original fallacies. Whatever we call this error, it shows up whenever you find this pattern:

  • If you live in Detroit, you live in Michigan
  • Therefore, if you don’t live in Detroit, you don’t live in Michigan.

This error is obvious when you use an intuitive example involving geography, but it is less obvious in other contexts. Don’t let that keep you from looking for it every chance you get–this little error is easy to slip into an argument and hard for the untrained eye to spot. That means you’ll see lots of these errors in easy-to-medium flaw questions.

You’ll see this answer choice often, but it may be the hardest answer to make sense of. The LSAT writers often use abstract terms that tend to paralyze the student. While it is possible to decode these baffling answers and demonstrate that they describe a “mistaken negation (TM),” it is very hard to do that with the clock ticking and your future on the line. That’s why it is so important to learn to identify this and other flaw answers before test day.

Here are some examples of answers that describe this particular flaw. (These are not actual LSAT answers, due to copyrights, but they are inspired by and similar to real answers):

  • “It treats a sufficient condition for an argument’s conclusion to be a necessary condition for that conclusion.”
  • “Takes a sufficient condition to be a necessary condition.”
  • “Mistakes something that is sufficient to make an argument invalid for something that is necessary to make that argument invalid.”

Basically, these answers all indicate that somebody confused a sufficient condition for a necessary condition. That sounds a lot like a “mistaken reversal (TM)” (which is what happens when you confuse a necessary condition for a sufficient condition), but it is different. If you think a condition is necessary, then not having that condition means you can’t have the other condition.  Here’s how that works out:

  • If you live in Detroit, you live in Michigan (true)
  • If you live in Michigan, you live in Detroit (false–you confused the necessary term for a sufficient term)
  • If you don’t live in Detroit, you don’t live in Michigan (false–you confused the sufficient term for a necessary term by saying what would happen if you didn’t have that term)

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