#2 - John: For 40 years, fluoride has been added to public

[prep88]

Hi everyone,

In this causal flawed stimulus the author states that "fluorid bone cancer" and concludes that "NO fluoride NO cancer". In real world sense this flaw is abvious but in LSAT don't we have a rule that if the cause (fluoride) is absent the effect cannot acure, because cause is THE ONLY cause for the stated effect? So that when there is no fluoride, there could be no bone cancer? In other words the claim is dismissed because there could be some other alternate causes??

Thanks!

[Robert Carroll]

prep,

The principle of interpretation is not that if the cause does not occur, the effect does not occur, but that the author, when making such a causal claim, is committed to saying (something like) "Fluoride is THE cause of bone cancer." That doesn't mean we agree with the author - in fact, because causal arguments are so easy to undermine, by the 5 methods for weakening causal arguments mentioned in the book, they're generally quite fragile. If something else could cause bone cancer, we aren't supposed to ignore that - we're supposed to point to that as the very flaw in the author's argument.

We don't have to believe the author that fluoride is the only possible cause - we don't have to go along with the author's flaw, but we can instead point out that it is a flaw because it ignores other possible causes. Thus, lacking the mentioned cause does not mean the effect will not occur. Only the author, erroneously, claims otherwise.

Robert Carroll

[prep88]

Yes, but this isn't even the author's oppinion, since it is a study result, which I thought we are supposed to take as true. Granted, if it was in the authors conclusion, it would be a common flaw, but this statement is a study result, a background fact how can we not believe it??

[Lucas Moreau]

Hello, prep88,

We are in fact taking the study result as true, but we don't really need to. I've bolded the important part in the author's conclusion:

"Even though I am healthy now, I should nevertheless stop drinking fluoridated water; only then will I be sure not to develop bone cancer."

Do you see the problem? He cannot be sure that he will not develop bone cancer, even if the study is accurate and fluoridated water does indeed cause bone cancer, just as a result of not drinking fluoridated water. He could just (seemingly) randomly develop it, or maybe he works with radioactive hazardous waste or something.

By declaring that he is safe from developing bone cancer by merely forgoing fluoridated water, that is the flaw in his argument. Note that this is true whether or not the study results are true - whether fluoridated water does cause bone cancer or not. It doesn't matter. All that matters is that other things cause bone cancer, thus gutting the author's claim.

Hope that helps,
Lucas Moreau

[prep88]

1. So, basically the statement in the second sentence "fluoride bone cancer" is true?
2. Is it true that in causal relationship the cause is the only cause for the stated effect and, by implication, the effect cannot occure without the cause?
3. If yes, how is this stimulus different from other causal stimuli?

Thanks a lot!

[Nikki Siclunov]

Hi prep,

Yes, the results of the study function as a premise in the argument, so they should be accepted as true:

Fluoride (cause) Cancer (effect)

That fluoride causes cancer is not under dispute. However, the study does not indicate that fluoride is a necessary cause of cancer: cancer can be caused by other factors, as Lucas and Adam already explained. So, by concluding that he can avoid cancer by not ingesting fluoride, John is assuming that fluoride is a necessary condition for getting cancer, i.e. that it is the only possible cause for cancer. In conditional terms, John's unwarranted assumption can be diagrammed as follows:

Cancer (sufficient) Fluoride (necessary)

This type of assumption is central to most arguments containing a causal error in reasoning. The correct answer to this Flaw question could also have stated:

John assumes, without warrant, that fluoride is the only possible cause of bone cancer.
John takes for granted that bone cancer can only be caused by fluoride.
John confuses a causal relationship for a conditional one.
John mistakenly infers a conditional relationship from a mere evidence of causation.

Hope this clears things up!

[kcho10]

Hello,

I think I might be confusing myself with the conditional reasoning in the conclusion. "I should nonetheless stop drinking fluoridated water; only then will I be sure not to develop bone cancer."

Does 'only then' mean the same thing as 'only if' on the LSAT? To me it seemed like 'only then' refers to the preceding clause/phrase, which would make 'I should stop drinking flouridated water' the necessary condition. But if that were the case, it seems like E wouldn't be much of a flaw.

[James Finch]

Hi KCho,

Yes, that's "only then" and "only if" are essentially interchangeable. John's conclusion is that he needs to stop drinking fluoridated water. Why? Because only fluoridated water can cause bone cancer, i.e. drinking fluoridated water is a necessary condition of developing bone cancer. John is making a sweeping claim here, that only by drinking fluoridated water can a human being contract bone cancer. But why does John believe this? The only reason he gives is the result of a single study on rats which almost all males and none of the females developed bone cancer after drinking fluoridated water.

This does seem to suggest that fluoridated water can cause bone cancer in male rats, but do we then know that it is the only possible cause of bone cancer in male rats, let alone in humans? No, this study alone cannot support such a sweeping claim, but unfortunately that's all the evidence that John gives us, so we're left with an argument that simply doesn't have enough evidence to support its conclusion. Only answer choice (E) exposes this flaw by mentioning the possibility of other causes for bone cancer, which would mean that even if he stopped drinking fluoridated water, John could still be at risk for it.

Hope this helps!

[Catallus]

I feel like I am somehow confusing sufficiency and necessity here and would appreciate some help!

(E) was suspicious to me because John states that "only" if he stops drinking fluoridated water will he "be sure not to develop cancer." So he says that not drinking fluoridated water is necessary—not sufficient—for certainty in not getting bone cancer. This seems valid: if drinking fluoridated water causes bone cancer (based on the study), then yes, a necessary condition for being sure not to get bone cancer is not drinking fluoridated water (sure not to get bone cancer --> not drink fluoridated water). But John doesn't seem to be making the (invalid) reversed claim that if he doesn't drink fluoride, then he won't get bone cancer (not drink fluoridated water --> sure not to get bone cancer).

Analogously, for example, I would think it's valid to say something like, "the only way I will be sure to avoid a cold is to wash my hands regularly." In doing so, I wouldn't be saying that I will avoid a cold if I wash my hands—simply that it's necessary to wash my hands to be sure of avoiding a cold, although there are probably other necessary conditions as well (get enough sleep, stay hydrated, etc.).

[Jeff Wren]

Hi Catallus,

The wording of the conclusion here is definitely tricky. This is a situation where the best approach is probably to look at the meaning of the sentence holistically rather than simply relying on the standard sufficient/necessary indicator words. (To be clear, those indicator words are a helpful guide in general.) Here, the words "to be sure" are conveying the idea of sufficiency. In meaning, the sentence would be equivalent to saying "not drinking fluoridated water is the only way to guarantee not to develop bone cancer." Since John is essentially stating that not drinking fluoridated water is the one and only way to guarantee not to develop bone cancer, you could consider this a biconditional in which each term is sufficient and necessary for the other.

The key flaw though is understanding the shift from causal reasoning to conditional reasoning and failing to recognize the possibility of alternate causes for bone cancer as Answer E describes.