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Some Pointers on Weakening: You can weaken by showing *inconsistency*

KevinLuminateLSATKevinLuminateLSAT Alum Member
edited August 31 in Logical Reasoning 827 karma

I noticed a few posts asking for tips on weaken questions, and was in the middle of writing a response. But I thought this would make more sense as a general post. If you're struggling with level 4 and 5 weaken questions, this might be helpful.

TL;DR = You can also weaken an argument by pointing out an inconsistency in the author's reasoning. It's not just about showing why the conclusion could be false despite the evidence being true. And it's not just about trying to directly counter the assumption.


As a preliminary matter, when weakening an argument, we're primarily trying to weaken the reasoning of the argument. That's something the curriculum emphasizes. But there are actually several ways by which one can weaken the reasoning of an argument.

One way is to directly counter the assumption. So, take this sample argument:

Penguins are chubby.
So, they're cute.

The assumption here is that if something is chubby, then it's cute. So we can weaken the argument by showing that there's at least one thing that's chubby that isn't cute.

(Now, if your instinct is to say, but that doesn't mean penguins aren't cute - they can still be cute. And chubbiness can still be one factor that contributes to their cuteness; it can still be a + on the scale of cuteness. You're right - but we've still weakened the argument by showing that their premise does not automatically prove their conclusion. The author of the argument was assuming that the chubbiness of penguins, by itself, without anything more, would guarantee their cuteness. We've shown that that assumption is wrong, which hurts the argument.)

That way of weakening an argument I think is most natural, and most susceptible to an approach that focuses on "Why could the conclusion be wrong even if the evidence is true?"

But another way to weaken reasoning is by showing that the assumption would lead to an inconsistency in the author's position. And this way of weakening is something that can escape one focused solely on pointing out a "loophole" (to borrow the parlance of the popular book). For example, let's add a bit to the stimulus:

Many animals in the world are not cute. Snakes, skunks, and rhinos, for example.
But, penguins are chubby.
So, penguins are cute.

One assumption of this argument is that if something is chubby, then it's cute. Do you see how we would weaken the argument by pointing out that rhinos are chubby? If we accept the author's assumption, then the author would compelled to think that rhinos are cute - but that contradicts something the author believes. But if we don't accept the assumption, in order to preserve the author's belief that rhinos are not cute, then the author's premise no longer leads to their conclusion about cute penguins. So we've caught the author in a contradiction - their affirmed position on rhinos conflicts with the assumption underlying their argument about penguins. Argument = weakened. Notice how if you go into the answers on this argument thinking "Why could penguins not be cute even if they're chubby?", you won't immediately notice the logic of the answer "Rhinos are chubby."

Now the example above demonstrates what one might call an "indirect" showing that the assumption is false. Rather than directly giving an example of something that's chubby but not cute, we've shown that the author's own beliefs commit them to something that contradicts that assumption - thus, the assumption is false.

Here's another version of "indirectly" showing that the assumption is false by way of inconsistency.

Devi said she'd be in Los Angeles at 9pm.
Thus, we can expect to see her in LA at that time.

We can weaken this argument by pointing out: "She said she'd be in San Francisco at 9pm." This weakens because if we accept the author's assumption that she'll be where she said she'd be, then she'd have to be in both LA and SF at 9pm. Clearly that's impossible, which means the assumption is wrong.

But this idea of inconsistency as a weakener also extends to situations in which we're not actually showing that the assumption is false.

Here's an example:

Sarah says that Paradorn, our new international student, was born in Thailand.
But his accent does not sound like that of someone born there.
Thus, Paradorn was probably born in a different part of Southeast Asia.

Now one way to think about this is to ask, "Why might he actually be from Thailand despite not having an accent that sounds like someone born there?" And if this your question, you'll be naturally disposed to answers that point out that you can be from a country without having an accent associated with speakers of that country. For example, he might have been born in Thailand but moved to a different place when he was young, which would explain his lack of an associated accent.

But what would you think about this answer: "Paradorn's accent does not sound like that of someone born in parts of Southeast Asia outside of Thailand."

This actually does weaken the argument, because the author's underlying assumption is that if one does not have an accent that sounds like that of someone born in a particular area, then that means one was probably not born in that area. By pointing out that his accent is not like that of someone born in SEA, we've caught the author in an inconsistency. According to their own assumption, we'd have to conclude that he probably wasn't born in the non-Thailand parts of SEA, either. But that goes against the author's own conclusion - so either the author's assumption is wrong, or the author's conclusion is wrong. Argument = weakened.

In my experience, this type of answer is a bit difficult to pick up on because most people would be mainly focused on showing why Paradorn actually could be from Thailand despite the lack of an accent. And it's tough to see how this answer gives us some positive reason to think he may have still been born in Thailand.

In addition, the logic of this answer seems to go against our initial instinct to question the relationship between being born in a particular place and having an accent associated with that place. Many of us would think "The lack of an accent doesn't really tell us much about where you were born." And then it would be weird to pick an answer that weakens by seeming to suggest that because he doesn't have an SEA accent, he's not from SEA. But the key is that this answer's logic isn't actually about countering the conclusion of the argument. It's about showing the author's inconsistency - if their assumption is true, then their conclusion doesn't make sense. And if their conclusion is true, then their assumption doesn't make sense. This does weaken the argument even if we have not actually shown that the author's conclusion is false or that their assumption is false. What we've shown is that at least one of them must be false.

This type of weakening logic, I think, is hard to recognize if your approach is limited only to asking "Why could the conclusion be false even if the premises are true?"

Comments

  • Matt SorrMatt Sorr Alum Member
    1615 karma

    Great post. Thanks for this.

  • AJamal22AJamal22 Monthly Member
    edited August 31 204 karma

    This is a great. Are there any weaken questions you know of throughout our practice where you have seen it be displayed and the correct answer is demonstrating inconsistency as opposed to weakening the support structure?

  • JY DiscipleJY Disciple Member
    223 karma

    This is very helpful, Kevin. Thank you for the examples, and explanations.

  • crustychikncrustychikn Alum Member
    14 karma

    The thing that always gets me is that for weakening questions I remember seeing that we shouldn't attack the premise / conclusion but for this example I feel like it's doing just that in a way. Can anybody please clarify this for me :)

  • TokhajaanTokhajaan Alum Member
    130 karma

    The loophole book.

  • Steven_B-1Steven_B-1 Monthly Member
    743 karma

    Wow, thanks for the thorough explanation! The examples were very helpful!

  • KevinLuminateLSATKevinLuminateLSAT Alum Member
    827 karma

    @crustychikn said:
    The thing that always gets me is that for weakening questions I remember seeing that we shouldn't attack the premise / conclusion but for this example I feel like it's doing just that in a way. Can anybody please clarify this for me :)

    Can you elaborate on which example you feel involves attacking the premise? Or attacking the conclusion directly?

    (Just as a side note, if an answer choice does in fact falsify a premise, it does weaken the argument. Similarly, if an answer choice does in fact show that the conclusion is false, I'd have to pick that as a weaken answer. So there's no rule against weakening in this fashion, even if these kinds of correct answers don't appear very often. In practice I'd have to say that I don't really think about this distinction between attacking the premise vs. attacking the assumption vs. attacking the conclusion, as there is no problem in which we have to decide between two answers, one of which validly attacks the premise or conclusion directly, and one of which attacks the assumption.)

  • KevinLuminateLSATKevinLuminateLSAT Alum Member
    edited September 1 827 karma

    @AJamal22 said:
    This is a great. Are there any weaken questions you know of throughout our practice where you have seen it be displayed and the correct answer is demonstrating inconsistency as opposed to weakening the support structure?

    I view demonstrating an inconsistency as 1 way to weaken the support structure, not as something separate. It's just that many would focus on directly falsifying the core assumption, without realizing that another way to weaken the support is to point out something that leads to an inconsistency in the author's reasoning.

    PT38 LR2 #15 (baja turtles)
    Rather than directly showing an example of how a 95% DNA match with X doesn't indicate that the origin is X, the correct answer weakens by showing that the author's assumption about what a 95% DNA match shows leads to a contradiction.

    PT35 LR2 #20 (projectile in mastodon)
    Rather than directly showing that the dissimilarity of a projectile to those found in area X doesn't prove that the first settlers didn't come from X, the correct answer weakens by showing that the author's assumption would go against their own conclusion, too.

    PT67 LR2 #24 (nightbird)
    Rather than directly showing that Larocque could still be the original author despite the lack of known orpiment use, the correct answer weakens by showing that the author's assumption would go against their own conclusion, too.

    One thing I'll note is that you could interpret the correct answer in all of these as falsifying an assumption, not necessarily as demonstrating an inconsistency. For example, in the Baja turtle problem, you could say that the argument is assuming both that a 95% DNA match indicates the origin of the turtles AND that the turtles don't have a 95% DNA match to any other location besides Japan. That's a fair way to view it, in which case the correct answer is just falsifying the second assumption. But I still think the notion of weakening by inconsistency is relevant here in that it's the entire reason one can say that the argument must assume there's no 95% DNA match to another location. If there were such a match, then the author's other assumption (that 95% DNA match indicates origin) would lead to an incoherent position (that the turtles came from both Japan and the other location).

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