#13 - Mayor: The law prohibiting pedestrians from crossing

[srcline@noctrl.edu]

Hello

I am having a hard time with this question I originally choose C, but the correct answer was D. My conditional chain was

Useful law must deter kind of behavior it prohibits
+: law must not deter kind of behavior is prohibits not useful

Is C incorrect because it is mistaken reversal?

Also I diagrammed the last part of the stimulus as

no law prohibit. pedes. never cross red lights

+ cross red lights there is law prohibt. pedes. from crossing against red lights ?

Also how would I quickly answer this problem, since I was caught b/w answer choices C./ D ?

Thankyou
Sarah

[Robert Carroll]

Sarah,

As this is a Flaw in the Reasoning question, the flaw must be contained in the stimulus. A Mistaken Reversal would be a flaw, so that answer choice (C) is a reversal isn't the reason it's wrong. The author did not use a Mistaken Reversal in the reasoning in the stimulus. This is the problem.

There is no error of conditional reasoning in the stimulus.

The author is claiming that the law serves no useful purpose because it does not deter the kind of behavior it prohibits. The author then talks about only two groups of people - those who always violate the law and those who never do. The flaw is in not talking about the group of people in between these extremes.

Robert Carroll

[bk1111]

Sarah,

As this is a Flaw in the Reasoning question, the flaw must be contained in the stimulus. A Mistaken Reversal would be a flaw, so that answer choice (C) is a reversal isn't the reason it's wrong. The author did not use a Mistaken Reversal in the reasoning in the stimulus. This is the problem.

There is no error of conditional reasoning in the stimulus.

The author is claiming that the law serves no useful purpose because it does not deter the kind of behavior it prohibits. The author then talks about only two groups of people - those who always violate the law and those who never do. The flaw is in not talking about the group of people in between these extremes.

Robert Carroll

Hello - C sounds like it would be a Mistaken Negation flaw? Is that correct?

[AthenaDalton]

Hi bk1111,

Both flaws involve an error in setting up the contrapositive. A mistaken reversal occurs where the sufficient and necessary terms are reversed, but not negated. A mistaken negation occurs where the sufficient and necessary terms are negated but not reversed.

I think (C) is best described as a mistaken reversal. This flaw is really just the flip side of the mistaken negation flaw -- you're on the right track!

[akanshalsat]

I'm a little confused as how C would have been a mistaken reversal?

I diagrammed it like this:

LUP (law to serve a useful purpose) ------>dbp (deter behavior it prohibits)

C says that the law might not serve a useful purpose even if it does deter the kind of behavior it prohibits = this makes sense bc, even if the necessary condition occurs (deters behavior it prohibits) its not guaranteed that the sufficient HAS to or WILL occur (law serving a useful purpose); so I don't get why this would be seen as a mistake? I just would look at it as something which is a valid thought that the mayor didn't see.

Also for D, I feel like the idea of the people "in between" doesn't jump out at me as much as C jumped out at me.. can someone please explain how we are to come to the conclusion that D is correct over C quickly?

Sorry for so many questions!

Best, Akansha

[Adam Tyson]

See Robert's answer earlier in this thread, akanshalsat - this is not a conditional reasoning flaw. The author did not say "if the law is useful, it deters, and this law deterred, so it is a useful," which would be a Mistaken Reversal, nor did he say "but it isn't useful, so it does not deter," which would be a Mistaken Negation. The flaw here is assuming that because the law has no effect on two groups of people - those who always obey and those who never obey - that it has no effect on anyone at all. That's a False Dilemma, not a conditional flaw.

(Side note: the author also presumes that those who always comply will continue to cross with the light, when they might not if the law did not exist.)

Also, answer C does not describe a conditional flaw. Instead, it just describes something that is true of all valid conditional claims - the necessary condition can happen even if the sufficient does not. That's not a flaw at all! That's another reason why it is not the correct answer, because the correct answer must describe an actual flaw.