LSAT 21 | Section 3 | Logical Reasoning: Q22

LR Question 22 Explanation

QUESTION TEXT: Anatomical bilateral symmetry is a common trait. It follows…

QUESTION TYPE: Parallel Reasoning

CONCLUSION: Bilateral symmetry must help organisms survive.

REASONING: It is common. Anything that is common must help organisms to survive.

ANALYSIS: This is a good argument. We’re given one sufficient necessary statement:

helps organism to survive ➞ common

We can take the contrapositive, and we get:

common ➞ helps organism to survive

So since bilateral symmetry is common, it helps organisms to survive.

The structure is: taking the contrapositive of a premise, and combining it with a known fact.

___________

1. There might be some other reason Sawyer was appointed. Maybe the city wants the negotiations to fail, and only Sawyer can be counted on to ruin things effectively.
2. This is a bad argument. It’s practically circular: its only evidence is that people think highly of Turnbull. But opinion can never prove a statement of fact.
3. CORRECT. The premise we’re given is this:
    
   No superior skills ➞ Not appointed
    
   Since Powell was appointed, she must have superior skills. This is the contrapositive combined with a known fact.
4. This isn’t a good argument. Rivers never negotiates unless Varga isn’t there. But that doesn’t mean rivers always negotiates when Varga isn’t there.
5. This is a good argument. It’s reasonable to expect Wong to be appointed, though it isn’t certain. But this doesn’t have the same contrapositive structure as the original argument.

Recap: The question begins with “Anatomical bilateral symmetry is a common trait It follows”. It is a Parallel Reasoning question. Learn more about LSAT Parallel questions in our guide to LSAT Logical Reasoning question types.