Mayor: The law prohibiting pedestrians from crossing against red light

We have pedestrian law that some people do not follow, while others who do follow it never need it because these people (who follow the law) would never cross against a red light, irrespective of whether there's a law or not.

But what if the presence of the law is the real reason why some people (among those who follow the law) actually end up following it? If such a law were absent, then some of these people will not have an incentive to avoid crossing against a red light (since they may assume that no law = perfectly legal to walk against red light). This is the logical flaw in the argument.


The mayor’s argument is flawed because it


(A) takes for granted that most automobile drivers will obey the law that prohibits them from driving through red lights - the argument is not centered on what the 'automobile drivers' do. Hence, eliminate (A)

(B) uses the word “law” in one sense in the premises and in another sense in the conclusion - the passage does not make such a distinction. Hence, eliminate (B)

(C) ignores the possibility that a law might not serve a useful purpose even if it does deter the kind of behavior it prohibits - In this passage, the "usefulness" of a law is being judged by its capacity to 'deter' the behavior it tries to prohibit. While some people may choose to violate a law, it still keeps others "safe". The safety of pedestrians is certainly a factor that needs to be considered when judging the usefulness of a law. So, if the pedestrian law deters at least some people from crossing against a red light, it might help protect these people from pedestrian related accidents, which could have no limits if such a law didn't exist in the first place. (C) does not hold merit. Hence, eliminate (C)

(D) fails to consider whether the law ever dissuades people who sometimes but not always cross against red lights - this is exactly what we are looking for. Hence, (D) is the right answer choice.


(E) provides no evidence that crossing against red lights is more dangerous than crossing on green lights - the distinction between red and green lights is irrelevant to the conclusion drawn. Hence, eliminate (E)

We need to find the flaw in reasoning.

Premise: Those who don't follow rules, will not follow law even if it is punishable.
Premise: Those who follow rules, will follow law even if it is not punishable
Conclusion: Ban the law

It fails to consider that there might be a segment of people who follow the law only because it is a law.

This flaw is clearly stated in Option D­

Mayor: The law prohibiting pedestrians from crossing against red lights serves no useful purpose. After all, in order to serve a useful purpose, a law must deter the kind of behavior it prohibits. But pedestrians who invariably violate this law are clearly not dissuaded by it; and those who comply with the law do not need it, since they would never cross against red light even if there were no law prohibiting pedestrians from crossing against red lights.

The mayor’s argument is flawed because it


(A) takes for granted that most automobile drivers will obey the law that prohibits them from driving through red lights

(B) uses the word “law” in one sense in the premises and in another sense in the conclusion

(C) ignores the possibility that a law might not serve a useful purpose even if it does deter the kind of behavior it prohibits - WRONG. Does not helps as it slightly diverts from the core(highlighted text) of the passage.

(D) fails to consider whether the law ever dissuades people who sometimes but not always cross against red lights - CORRECT. It elaborates something that may have served the purpose that the law must have had.

(E) provides no evidence that crossing against red lights is more dangerous than crossing on green lights

Answer D.