Mistaken Reversal/Negation

[jgray]

Greetings,
In Mistaken Reversal, Sufficient and Necessary are reversed, but not negated?

In Mistaken Negation, Sufficient and Necessary are negated, but not reversed?

Both are one step away from being correct?

[Steve Stein]

Hi Jgray,

You got it! A mistaken negation is a negation in which you forgot to reverse, and a mistaken reversal is a reversal in which you forgot to negate. Both, as you stated well, are just one step away from being correct.

Nice! Let us know if you have other questions as you continue your preparation--thanks!

~Steve

[jgray]

In regards to applying these terms to flaw in the reasoning questions.

I understand what the flaws look like diagramed, and I can identify contenders for the right answers. However, I’m not able to clearly understand what the authors are really saying. Can you elaborate how the LSAT authors present mistaken negation and mistaken reversal in the answer choices? Obviously, they are not simply stating the confusion between the necessary condition with the sufficient condition (mistaken reversal?).

[Dave Killoran]

Hi J,

I'm traveling at the moment so I'll be brief, but perhaps one of my colleagues will get the chance to add some more in the interim.

By appearance, the two flaws look very different. But, from a logical standpoint, they actually revolve around the same basic error, which is actually the one you mention: the confusion between what actually is sufficient and what is necessary. Reversals and Negations thus tend to be described in exactly those terms. For example, on the December 2014 LSAT, LR2, #22, the correct answer to a Flaw question featuring a Mistaken Negation is "takes a sufficient condition as a necessary one." Or, this language from September 2014, LR2, #25 for a Mistaken Reversal in a Flaw question: "takes a necessary condition for...a sufficient condition."

Why is is that the errors can basically be described in similar ways? Well, despite their different appearance, at the root they are the same error. And this can be seen by realizing that the MN of a statement, and the MR of that same original statement, are actually contrapositives of each other. As we know, a statement and its contrapositive are fundamentally identical, and so a Mistaken Negation and a Mistaken Reversal are really the same basic idea expressed in different ways. That's pretty tricky, right? It's also the reason that in a Parallel Flaw question that features an MN or an MR, for example, you won't typically see both an MR and an MN in the answers; you'll just see one.

The above just touches the surface, but it's something to think about. The bottom line is that when you see a conditional flaw in the stimulus and then it gets paired with a flaw question, if you see an answer that talks about mixing up the conditions, that's probably the right answer (but compare it to the others to make sure they don't slip a little extra in there that makes it wrong).

Please let me know if that helps. Thanks!

[jgray]

Yes, that does help. I’ll keep this in mind as I continue training.

[lathlee]

Yeah this puzzles me as i was going over cannot be true question stem Q card Drill. One drill in a LR Bible Ex, All Doctors are wealthy

So the correct expression is D W .
Its cotraposive : (Negation) W (Negation) D.

I know my following concept that i bring up was disucced recent version of LR Bibles Principle Chapter of version 2016 and forward, but i still have a problem comprehending the correct grasp time to time.

In this context,
While (negation) W D is clearly cannot be, its logical equivalent, contrapositive : (negation) D W , could be or possible.

[Malila Robinson]

Hi lathlee,
When I was first learning Conditional Reasoning it helped me to talk through everything as If/Then statements. So in your example we have:
If you are a doctor, then you are wealthy.
CP: If you are not wealthy then you cannot be a doctor. (since all doctors must be wealthy)

In the possibilities you have brought up:
If you are not wealthy then you must be a doctor. (impossible since all doctors must be wealthy)
If you are not a doctor then you are wealthy. (possible, because we didn't say that the only wealthy people are doctors, so people other than doctors may also be wealthy)

Hope that helps,
-Malila

[davidp95]

Are all mistaken reversals mistakes a necessary for sufficient and are all mistaken negations mistakes a sufficient for necessary?

Many forums state that a mistaken reversal is when you mistake a necessary condition for a sufficient condition and that te mistaken negation is the opposite.

Is this always the case?

Mike Kim gives an example that seems to contradict this rule: "If you finish college, you are certain to be financially successfully. Therefore, if you want to be be financially successful, you must finish college" In his book. he states that this is Mistakes a sufficient for a necessary"

He gives other examples such as " Coffee helps one stay awake. Therefore, if one wants to stay awake one needs to drink coffee" or "Every student in Mrs. W class went to the museum. Since Sean went to the museum, he must be in Mrs. Wilber' Class"

These all seem to contradict the idea that mistaken reversal are all mistakes a sufficient for necessary

[Rachael Wilkenfeld]

David, they are both essentially the same error.

For example, in your statement "If you finish college, then you are certain to be financially successful."

Finishing college is sufficient. Financially successful is necessary. Showing an example where someone is financially successful, and concluding that they must have finished college is both errors. It's mistaking the sufficient condition (finishing college) for the necessary condition (financial success) by putting finishing college as necessary for financial success. It's also mistaking the necessary condition (financial success) for the sufficient (finishing college) by stating that financial success is enough to prove that someone has finished college.

Hope that helps!

[davidp95]

Thank you so much for the reply Rachel!

It does helping in that they are both essential switched.

My apologies I was not clear on how I was confused. It's knowing the difference between the answer choices:

"Mistakes a necessary condition for a sufficient condition to reach the conclusion"

Vs

"Mistakes a sufficient condition for a necessary condition to reach the conclusion"

Is it essential that the first one assumes uses the necessary condition guarantees the outcome? So using the college example: since you are financially successful , you went to college.

And for the other: you are financially successful because you must have went to college