LR Question 9 Explanation
QUESTION TEXT: If a mother’s first child is born before its due date…
QUESTION TYPE: Flawed Parallel Reasoning
CONCLUSION: Jackie’s first child probably wasn’t born before the due date.
REASONING: 1st child born before due (most) ➞ second child born before due.
Jackie’s second child wasn’t born before due.
ANALYSIS: “Likely” is a synonym for most. So this argument gives us a “most” statement, then tries to take the contrapositive. But you can’t take the contrapositive of a “most” statement the way you can for a conditional statement. That’s because there can always be exceptions to a “most” statement.
(A conditional statement is one where the sufficient condition always leads to the necessary condition)
The answers are a bit technical. I’ll give examples. Take this statement:
Cat ➞ has tail
- Incorrect reversal: tail ➞ cat
- Incorrect negation:
cat➞tail - contrapositive (correct)
tail➞cat
Now, this argument uses a “most” statement. You can’t do any of these with a most statement. Even contrapositives. This argument is wrong because it tries to reverse and negate a “most” statement. You need to find the answer that does the same thing.
___________
- This incorrectly negates a “most” statement. That’s not the same as trying to take the contrapositive of a “most” statement.
- This incorrectly reverses a “most” statement. That’s not the same thing as trying to take the contrapositive of a “most” statement.
- CORRECT. This reverses the terms of a “most” statement, and negates those terms. This is the same error as the stimulus – you can’t take the contrapositive of a “most” statement.
- This is a good argument. Unlike all the other answers, this one has a conditional statement. In every case where a business is likely to fail, people won’t invest.
- This incorrectly reverses a conditional statement and adds a “probably”.
Recap: The question begins with “If a mother’s first child is born”. It is a Flawed Parallel Reasoning question. To practice more Flawed Parallel Reasoning questions, have a look at the LSAT Questions by Type page.
More Resources for Flawed Parallel Reasoning Questions
- Conditional Reasoning Article: Learn about conditional statements.
- LR Diagrams Guide: Learn how to draw LR diagrams.
- Flaw drills: Practice identifying flaws.
- Intro Course lesson: This intro course lesson covers Flawed Parallel Reasoning questions.
- Mastery Seminar lesson: This LR Mastery seminar lesson covers flawed parallel reasoning questions.
Hi there,
If, instead, the argument is “It is unlikely that Jackie’s second child will be born before its due date, so Jackie’s first child is not born before its due date,” then that would be a valid argument, right?
Thanks!
Close but yes, if it said “was not born”. This works because being born early is a sufficient condition for the second child’s early birth being likely.
If that isn’t the case then the first child must not have been born early.
Thanks a lot Graeme!
May I follow up a bit, is the underlying logic here the same as your comment on Preptest 73>>Logical Reasoning 1 >>Question 4?
(I tried to add the link to that page here. But the site won’t allow me to post my comment with the link. It seems to be an anti-spam mechanism).
Had a glance, looks like similar logic. Sufficient condition –> likely
Thanks Graeme!
Hi Graeme,
Just starting out on LR questions, I end up eliminating answers by matching the tenses and probability. For example, answers B and E use statements without uncertainty in their opening line and answers A and D both use the future tense (“Will”) in their first line. The wrong answers do have some other indicators that they aren’t parallel, but is this tense and uncertainty matching a good strategy? Or is it setting me up to be fooled?
Thanks for your time
Yes, tense and certainty are very good bets. They don’t prove and answer is right all by themselves, but I will often filter answers based on factors like this and choose 1-2 answers to test. Then I compare only these answers to the stimulus more thoroughly. So use these factors to filter though never treat them as indicating an answer is for sure right or wrong in isolation. Parallel often uses multiple factors.
Note: This is an old comment but I wanted to clarify the point.