LSAT and Law School Admissions Forum

Get expert LSAT preparation and law school admissions advice from PowerScore Test Preparation.

 Administrator
PowerScore Staff
  • PowerScore Staff
  • Posts: 8225
  • Joined: Feb 02, 2011
|
#23161
Complete Question Explanation

Flaw in the Reasoning. The correct answer choice is (D)

Here we are told initially that Sara probably has the same illness as Michael does. Based on this premise, the information that Michael does not have streptococcal infection is treated as absolute proof that Sara does not have streptococcal infection. Therefore the answer choice will have something to do with the problem of using probability in an effort to prove something as fact.

Answer Choice (A) The argument does not presuppose that Sara does not have streptococcal infection; it simply uses flawed reasoning to get to that conclusion.

Answer Choice (B) There is no issue of causal reasoning here. The issue is not what caused Sara to get an illness, it is an issue of determining exactly what illness she has.

Answer Choice (C) The stimulus is not concerned with how severe Sara's case of streptococcal infection may or may not be. It is only concerned with whether or not she has the illness.

Answer Choice (D): This is the correct answer choice. Based on the fact that Sara and Michael probably have the same disease, we can say that Sara probably does not have streptococcal infection based upon the fact that Michael does not have it. We cannot, however, establish that claim as fact based upon the information provided.

Answer Choice (E) There are no general claims here and no respective groups that the stimulus reasoning is intending to represent. Instead, a very specific claim is being made about a very specific person — that Sara does not have streptococcal infection.
 lathlee
  • Posts: 655
  • Joined: Apr 01, 2016
|
#40856
Hi. Is this number and probablity reasoning flaw? I don't think it is. I never saw question error like this , so want to know why. I got this question correct eventually by ruling out all the incorrect ones but still bothers me a lot.
 lathlee
  • Posts: 655
  • Joined: Apr 01, 2016
|
#40938
----
Last edited by lathlee on Sun Mar 25, 2018 8:28 am, edited 1 time in total.
 Francis O'Rourke
PowerScore Staff
  • PowerScore Staff
  • Posts: 471
  • Joined: Mar 10, 2017
|
#41008
Hi Lathlee,

This flaw is an Error in the Use of Evidence. The speaker uses some evidence for the conclusion to try to show that the conclusion must be true. The evidence is inconclusive, yet the speaker treats it as if it were conclusive.
 Nicholas Noyes
  • Posts: 38
  • Joined: Feb 07, 2020
|
#74305
Hello,

So this argument is flawed because it says Sara "probably" has the same illness as Michael. But in the conclusion it says that they both defiantly do not have a streptococcal infection? Could you please help me clarify this please?

Thank You,
Nicholas
 Paul Marsh
PowerScore Staff
  • PowerScore Staff
  • Posts: 290
  • Joined: Oct 15, 2019
|
#74324
Hi Nicholas! So the flaw in the argument is not exactly the fact that it says Sara "probably" has the same illness as Michael. Rather, it's the disconnect between the "probably" in the premises of the stimulus, and the "definitely" in the conclusion. Let's walk through it:

For Flaw questions, we're looking for an error in the way that the conclusion is drawn from the premises. The conclusion here is "the illness Sara has is definitely not a streptococcal infection either." Very strong language like "definitely" in a conclusion should cause your inner alarm to start going off! Is there anything in the premises to indicate that Sara "definitely" doesn't have a streptococcal infection? No. We have some premises that lead the author of the stimulus to make the sort of intermediate conclusion that "Sara probably has the same illness as Michael". Based on this intermediate conclusion, and the fact that Michael doesn't have a streptococcal infection, the author of the stimulus could have correctly made the conclusion that Sara probably doesn't have a streptococcal infection. Instead, the author went too far and asserted that Sara "definitely" doesn't have a streptococcal infection.

Here's a simple example using the same flawed reasoning: "John and I probably have the same type of dog. I have a poodle. Therefore John definitely has a poodle."

The Flaw here is the disconnect between "probably" in the premises and "definitely" in the conclusion, since it is a Flaw for a conclusion to go beyond what the premises allow. Answer Choice (D) correctly points this Flaw out. Hope that helps!

Get the most out of your LSAT Prep Plus subscription.

Analyze and track your performance with our Testing and Analytics Package.