Logical Reasoning

PT111 · S4 · Q13 Mayor: The law prohibiting pedestrians

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Mayor: The law prohibiting pedestrians from crossing against red lights serves no useful purpose.

Conclusion

The law prohibiting pedestrians from crossing against red lights serves no useful purpose.

Evidence (after all)

To serve a useful purpose, a law must deter the behavior it prohibits.

Assumed Intermediate Conclusion

The law prohibiting pedestrians from crossing against red lights is not deterring people from crossing against red lights.

Evidence (since)

People who always violate this law (they always cross against red lights) are clearly not deterred by the law.

And people who always comply with the law (they never cross against red lights) would never be crossing against red lights even if there weren't a law, so they are also not being deterred by the law.

Evaluate

The author is trying to prove her conclusion with some "damned if you do, damned if you don't" binary logic.

If you're X, then you're Y. And even if you're not X, then you're Y. Thus, you're guaranteed to be Y.

Here, this sounds like this:

If you always cross against red, not deterred by this law. If you never cross against red, not deterred by this law. Thus, this law ain't deterring anybody.

However, in the first example, it was a true binary: X vs. not-X.

In this argument, it's not a true binary: always cross against red vs. never cross against red.

What about the people who sometimes cross against red? We're not being told whether this law could have any deterrent effect on them.

Goal

The author is arguing that since this law doesn't deter the behavior it prohibits, it serves no useful purpose.

We can't argue with that connection because there is a stipulated premise that "if doesn't deter, then serves no useful purpose".

Our only means for objecting is to argue that this law does actually deter the kind of behavior it prohibits. It would be hard, based on the premises, to argue that people who always crossed against red or who never crossed against red would be deterred by this law, but we could argue that other people are deterred by this law.

13.

The mayor's argument is flawed because it

  1. takes for granted that most

    Out of Scope: auto drivers

    This argument is only about a law about pedestrians. The author has made no assumptions about drivers.

    3% picked this

  2. uses the word “law” in

    Not Equivocation

    This answer describes one of the 10 Famous Flaws, Equivocation, in which a key term or concept is used in two completely different ways. This answer is almost never correct, and we should only pick it if we feel we can supply two very different definitions for the different instances of that word/concept. But here, the term "law" is consistently used to mean an enforceable statute written by a legislative body.

    1% picked this

  3. ignores the possibility that a

    Not an Objection

    This answer begins with fails to consider / ignores the possibility, so we check to see whether the idea that follows would Weaken or sound like an objection. Can we object to this author and say, "Hey, author. Even if a law did deter the kind of behavior it prohibits, it could still fail to serve a useful purpose." Nope that doesn't weaken. That actually strengthens, because the conclusion is that this law fails to serve a useful purpose. If we expand the number of cases in which laws fail to serve a useful purpose, we're giving this author's conclusion a better chance of being true.

    20% picked this

  4. Correct

    fails to consider whether the

    Why this is right

    This answer begins with fails to consider / ignores the possibility, so we check to see whether the idea that follows would Weaken or sound like an objection. Can we object to this author and say, "Hey, author. This law successfully dissuades people who only-sometimes cross against red lights." Yes, that's a big objection. That would allow us to say, "So this law does deter the kind of behavior it prohibits, at least somewhat. So this law may actually serve a useful purpose!" Again, in terms of reasoning archetypes, this author was committing a False Choice, an imagined binary, between people who always violate the rule and never violate the rule. She failed to consider another segment of the population. She failed to consider the middle ground between those two extremes.

    Skill tested: Flaw · how this choice captures the argument's function is the move to repeat next time.

    75% picked this

  5. provides no evidence that crossing

    Not an Assumption

    This answer begins with takes for granted / fails to establish / provides no evidence that, so we check to see whether the idea that follows was something the author needed to assume. Did this author need to assume that crossing against red lights is more dangerous than crossing on green lights? No, because she's not trying to justify the value of this law. The people who wrote the law forbidding crossing against red lights are clearly assuming that crossing against red is worse than crossing on green. But this author is arguing that the law serves no useful purpose, so there's no reason she needs to agree that it's worse to cross on red.

    1% picked this

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