Environmentalist: When bacteria degrade household cleaning products, vapors that are toxic to humans are produced. U...

Alyona on February 7 at 06:35PM

Problem with identifying necessary assumption.

Hi team, I found a pattern in mistakes I make on necessary assumption questions. Here is the thing, I've learned that Necessary assumption is either a Defender (that eliminates all other options) or a Strengthener that bridges a gap between conclusion and the premises. In this example I picked B for the reasons stated above. I keep doing this mistake with other questions, too. Please help me. It seems like I am implementing the idea of a necessary assumption as a Defender in a wrong way. Could anyone from your team help me out with this, please?

5 Replies

Alyona on February 7 at 06:58PM

I meant that a Defender eliminates all other possible causes of effect to happen. I've read it in the LR Bible. The rule states: when Assumption Q-n + Causality = correct answer choice eliminates alternative cause for the stated effect.
Where is mistake in understanding this rule?

Andrea on February 8 at 01:58AM

Hi @Alyona1983,

Which LR bible are you referring to? Unfortunately, I'm not familiar with the specific teaching technique you're referencing here. Is it described somewhere in their course? If so, could you let me know where so I can take a look for more context on your question here?

That being said, there is a more intuitive way to approach necessary assumption questions. Personally, I like to teach that approach. Think of a necessary assumption as a piece of information that you NEED to be true in order for an argument to even be possible. It doesn't have to prove the argument is true, because that's what a sufficient assumption does. Rather, necessary assumptions are just the bare minimum you need for your conclusion to even have a chance based on the information you're given. If that assumption weren't true, the argument wouldn't even be possible, which is why it's considered "necessary" to the argument. That's also where we get out negation technique from - if that answer choice weren't true, would that then destroy the viability of the argument? If so, then we know that answer choice is necessary to it!

Let's take a look at the question you have here. It's a necessary assumption question.

Our conclusion is that the practice of converting landfills into public parks is damaging human health. Why? Because bacteria release toxic fumes when they break down household cleaning products, and household cleaning products are found in landfills.

Isn't there a part of that explanation that seems to be missing? Something unstated, that you would need to also know in order to say that converting landfills into public parks is damaging health?

I can think of a couple things you might need to know. The first is that those toxic vapors are actually toxic enough, or at least found in high enough quantities, to be damaging to human health. For a lot of toxins, it takes more than a trace amount to really impact health. Another thing that we would need to know is that there isn't something else in the landfill that might be destroying the bacteria that does this. Truly, there are lots of things you would need to know to draw this conclusion. Our correct answer only needs to identify one of them, and it's our job to identify that option as being an assumption that's required for the argument to work. The rest of the answer choices won't be required by the argument.

A) Great! You need to know that there are bacteria actually there to cause this phenomenon in the first place.
B) It's not necessary to the conclusion to say that vapors are the only way damage can be caused to human health in these circumstances.
C) There are many ways humans could be exposed to vapors from household cleaning products, we only care that the bacteria way we’re given can damage human health.
D) Out of scope, skirts around our conclusion instead of addressing it. Not necessary to it.
E) "Any" is too strong. Since this is a necessary assumption, we only need to prove for at least one.

Hope this helps!

Alyona on February 8 at 04:38AM

Andrea, the bible is one of three books published by LSAC, this is how people would study for LSAT before online courses appeared on market :-) old classic method of studying.
Regarding answers, for some reasons I thought it is essential to make sure that the vapors are the only way damage can be caused to human health, that's why I was so attracted to B. But B would work for sufficient assumption, not the necessary one, right? And yes, I clearly see why A is the correct answer.
Thank you once again, I feel greatly supported by your incredible team. You've done a lot of work within the last two years, great job guys! My friends are happy with BarMax as well.

Andrea on February 8 at 05:56AM

Hi @Alyona1983,

Let’s diagram B out so you can see what it means a little better. Here is the diagram and it’s contrapositive.

Toxic vapors are not produced in a landfill and humans are not exposed to them —> converting that landfill into a public park will cause no damage to heath

Converting a landfill into a public park causes damage to health —-> toxic vapors are produced in that landfill and humans are exposed to them

As you can see more clearly from the second diagram, this argument doesn’t rely on vapors being the only way damage is caused. However, B doesn’t guarantee the truth of the argument, either, because the sufficient condition of the diagram above assumes the truth of the conclusion. This argument is trying to PROVE that converting a landfill into a public park causes damage to health. So, we can’t say this answer choice is sufficient to prove the conclusion when the conclusion itself is being used on the left side of the arrow. You have to end up at the conclusion, not start at it.

Hope this helps clarify for you! Let me know if you have anymore questions :)

Alyona on February 10 at 06:20PM

Thank you, Andrea, I found the flaw in my thinking now. Necessary os not the only necessary condition, there are/could be many of them, and proving that it's the only one is not needed for the necessary assumption question. Thank you for your time helping me out!