LSAT 2 | Section 4 | Logical Reasoning: Q20

LR Question 20 Explanation

QUESTION TEXT: Normal full-term babies are all born with certain instinctive…

QUESTION TYPE: Parallel Reasoning

CONCLUSION: This baby is not a normal full-term baby

REASONING: All normal full-term babies are born with certain reflexes that disappear by the age of two months. This baby is three months old yet still displays those reflexes.

ANALYSIS: This is a good argument. It has the following, contrapositive structure:

Every X isY. This thing is not Y, therefore it isn’t an X.

___________

1. This is a bad argument. Carbon dioxide will turn limewater murky, but there could be other ways of turning limewater murky.
2. This is a good argument. However, to mirror the structure of the stimulus we should be concluding that something isn’t an ape. The stimulus uses contrapositive reasoning.
3. This is a bad argument. Many people are both sociable and deeply, deeply weird. Social is a necessary condition for being human and nothing more.
4. CORRECT. This is a good argument. O P is the premise. We then use the contrapositive “does not have a pouch” to prove the conclusion “is not an opossum.”
5. This is a bad argument, because we only know that some trees shed their leaves annually.

Recap: The question begins with “Normal full-term babies are all born with certain instinctive”. It is a Parallel Reasoning question. Learn more about LSAT Parallel questions in our guide to LSAT Logical Reasoning question types.