LSAT 108 | Section 2 | Logical Reasoning: Q2

LR Question 2 Explanation

QUESTION TEXT: John: For 40 years, fluoride has been added …

QUESTION TYPE: Flawed Reasoning

CONCLUSION: I can only be sure that I won’t develop bone cancer if I stop drinking fluoridated water.

REASONING: It caused bone cancer in lab rats.

ANALYSIS: My brother gained weight from eating McDonalds. So I should stop eating McDonalds – only then will I be sure not to gain weight!

No. That’s silly. McDonalds isn’t the only possible cause of weight gain.

The same thing goes here. John acts as if fluoridated water is the only possible cause of bone cancer. But even if fluoridated water can cause bone cancer, there may be other causes as well.

Avoiding one possible cause doesn’t guarantee you’ll never get the disease.

___________

1. The argument is about whether John should stop drinking fluoridated water, not about other people.
2. Whether fluoridated water causes other diseases is irrelevant. His conclusion concerns bone cancer.
3. Brief periods without fluoridation during the last 40 years have nothing to do with whether John can be sure he won’t develop bone cancer.
4. Ignoring the benefits of fluoridation might affect whether stopping is a good tradeoff, but it doesn’t address the major logical flaw about certainty.
5. CORRECT. John fails to consider that bone cancer may have other causes. Even if avoiding fluoridated water eliminates one risk factor, it doesn’t guarantee he won’t develop bone cancer.