65.1.21: "Necessary" Assumption Forum

[LexLeon]

The stem asks for the assumption that the argument "requires."

I propose that the CR is not an assumption that is required by the argument; though it is clearly the best answer, and is, moreover, sufficient when added to the premises to draw the conclusion.

If you're interested in helping me to resolve my inquiry, please read the question and answer choices and then consider any of the following scenarios, none of which are ruled out by the information in the stimulus, but when assumed render the CR unnecessary.

1. The trees planted in response to the incentives absorb carbon dioxide that would otherwise be trapped in the atmosphere, but in turn emit more of it than they've absorbed.

2. The trees planted in response to the incentives emit a biological compound that causes native grasses to die, thereby exacerbating the atmospheric CO2 conditions, though none of the trees planted are planted where native grasses would otherwise be growing.

3. The trees planted in response to the incentives were planted in very great numbers, died quickly, and in decomposing contributed largely to a net increase in atmospheric CO2.

...I can think of any number of these, or tweak the above three an in infinitude of ways. Any of them, I claim, show that the CR is not really necessary.

I would like for someone either to correct me, and show me why the CR is actually required; or agree with me and share in my puzzlement, after having read the above argument.

[Taus11]

Haha what in the world are you thinking about all those possibilities for? Stick to the argument core. Seriously. That's how you solve necessary assumption questions. I am not going to take my time to go over those scientific possibilities because they are simply out of scope and irrelevant to filling in the gap in this specific argument.

Conclusion -> The government incentives of planting trees on their land are making the global warming worse.
Premise -> A recent study indicates that trees absorb and store CO2 less effectively than native grasses.

How does the fact that trees are less effective than native grasses enable a conclusion that trees are making the situation worse? If trees are planted somewhere else other than where native grasses, the argument states that they will absorb CO2 that might otherwise be trapped in the atmosphere. Your job is not to argue with or come up with alternatives to the premise. You are given that the trees will help by doing this. Therefore, the conclusion cannot hold if without the correct answer choice.

[Micdiddy]

Haha what in the world are you thinking about all those possibilities for? Stick to the argument core. Seriously. That's how you solve necessary assumption questions. I am not going to take my time to go over those scientific possibilities because they are simply out of scope and irrelevant to filling in the gap in this specific argument.

Conclusion -> The government incentives of planting trees on their land are making the global warming worse.
Premise -> A recent study indicates that trees absorb and store CO2 less effectively than native grasses.

How does the fact that trees are less effective than native grasses enable a conclusion that trees are making the situation worse? If trees are planted somewhere else other than where native grasses, the argument states that they will absorb CO2 that might otherwise be trapped in the atmosphere. Your job is not to argue with or come up with alternatives to the premise. You are given that the trees will help by doing this. Therefore, the conclusion cannot hold if without the correct answer choice.

He's not trying to discover the right answer to the question. He's arguing that it doesn't follow logically to call the assumption "necessary," because, he states, it is actually "sufficient" (when taking along with the rest of the premises.
I'll look at it now too...

ETA: So, I think the answer to the question is that this assumption is not necessary to reach the conclusion, it's simply the necessary link between the premises stated and the conclusion. The word "therefore" plays an important role, indicating the author is directly taking what was said before and claiming it proves the conclusion. Without the word "therefore," if it was just an uncoordinated presentation of premises and conclusions, then there would be many assumptions that could do the trick. But assuming the argument has to be based on the relationship between trees and native grasses, the assumption is necessary. amirite?

[Taus11]

Hm, I don't quite understand the issue here. Sufficient and necessary assumptions are not mutually exclusive. I didn't even attempt to think whether it was sufficient or not, just simply looked for a necessary one while I was taking it.

[chesterfan1230]

I think it serves as both, a sufficient and necessary assumption. It links the argument and is also necessary to make the argument.

[Micdiddy]

Hm, I don't quite understand the issue here. Sufficient and necessary assumptions are not mutually exclusive. I didn't even attempt to think whether it was sufficient or not, just simply looked for a necessary one while I was taking it.

Right, because you were just looking for the right answer. OP is not interested in the LSAT answer to this question, he is solely interested in their labeling it necessary.

And I agree with above that sufficient and necessary are not mutually exclusive, but that doesn't mean its ok to label something necessary when it's not. In this case, I agree it is both necessary for the cohesion of the particular argument structure the stimulus took, then sufficient along with those premises to prove the conclusion.
But it certainly not necessary for the conclusion to be true, strictly speaking.

Why do I feel like Timmydoeslsat right now??

[VasaVasori]

.

[Clearly]

Oh god it's Timmydoeslsat again...

[LexLeon]

All of your examples assume things outside of the context of the argument.

Every example you supplied is completely outside of the scope of the argument.

[...]

How do you link that to 3? You need to establish that trees are, indeed, replacing grasses.

That trees were somehow causing the destruction or absence of native grasses, perhaps by replacing them, is in no way outside of the scope of the argument. You just stated that above. The CR is a formulation of this proposition. Indeed it links the premise(s) to the conclusion.

My criticism is that, the way in which the CR is formulated is not required by the argument. The simple, analogous case that the planted trees competed for resources with the nearby grasses, causing them to die, serves the same function as the CR, and renders it not required.

Do you claim that the case I just mentioned is not an assumption required by the argument? Because if you do, then you also claim that the CR is not required by the argument. You'd be correct.

It should be pretty clear both that the analogous case above is sufficient for the argument's conclusion, but not necessary to it, just as the CR is, and, if assumed, would mean that the CR need not be assumed, indicating that the CR is not required.

I am not going to take my time to go over those scientific possibilities because they are simply out of scope and irrelevant to filling in the gap in this specific argument.

[...]

Therefore, the conclusion cannot hold if without the correct answer choice.

Please see above case, which is clearly within the scope of the argument, which when assumed enables the conclusion to be drawn, even if the credited response is logically negated.

[cc.celina]

The simple, analogous case that the planted trees competed for resources with the nearby grasses, causing them to die, serves the same function as the CR, and renders it not required.

If I may offer my interpretation: The argument proceeds first by noting that trees absorb CO2 less effectively than native grasses, and concludes from this study that these incentives help hasten global warming. (In fact, it is the only evidence in the entire stimulus that lends support to its conclusion.) The three possibilities in your original post, while they would be sufficient to render the conclusion true, do not do what the question asks: render the conclusion true on the basis of the single premise that is presupposed to support it.

In other words, the question stem does not read, "The conclusion requires the assumption that," but "the argument requires the assumption that."

In other words, yes, many things could be assumed to be true in order to render the conclusion true. Only one assumption is necessary to "trigger" the conclusion with some basis in the single premise offered in support of it - that trees are less effective than grasses.

I have quoted the assumption above because it is the only one I find satisfactory to possibly challenge the validity of the CR. If you assumed that trees competed for resources with nearby grasses, that would be sufficient without explicitly assuming the CR to render the conclusion true based on the premise.

However, I'm going to argue that it's simply rephrasing the CR. The CR is not that "farmers would have intentionally planted native grasses, but are otherwise planting trees." It is simply that trees are growing in places that native grasses would otherwise be growing. If a tree, planted in a specific spot, competes with the grasses around it for resources and thereby causes those grasses to die, then it has been planted where native grasses would otherwise be growing. I think it would be ridiculous to assume that the scope of the CR is limited only to where the tree's trunk sprouts up out of the ground - if the tree's roots are sucking water and nutrients out of the ground in a certain radius, I think it's fair to say that the tree is growing in that radius, and any grasses that would have grown in that radius had the tree not been there can be classified as grass that would have otherwise been growing.

Feel free to debate this

[bp shinners]

My criticism is that, the way in which the CR is formulated is not required by the argument. The simple, analogous case that the planted trees competed for resources with the nearby grasses, causing them to die, serves the same function as the CR, and renders it not required.

Do you claim that the case I just mentioned is not an assumption required by the argument? Because if you do, then you also claim that the CR is not required by the argument. You'd be correct.

You're arguing outside the scope of the LSAT.

For the purposes of the LSAT, a necessary assumption is one that is required to prove the answer choice based on the premises presented - the argument as written, not the argument with any external possibilities thrown in. Throw out all the possibilities you listed, because if the author of the argument wanted to talk about those, he would have mentioned that stuff in the stimulus.

Instead, he says that the trees are less efficient than the grasses. Therefore, we're hastening global warming by giving incentives to plant these trees. Based just on what the author of the argument is saying, we need to assume that some of the trees are replacing the grasses.

I'm not going to argue with anything that you've said. Instead, I'm going to just let you know that a necessary assumption for an argument, as defined by the LSAT, is going to deal with the premises presented, and not with any possibility you can come up with for connecting the two. It's not your job to make the prosecution's case for them, so to speak - if they haven't introduced something into evidence, don't put it in there.

As an example of this, let's look at your #2. That's a theory that certainly isn't contradicted by anything in the stimulus. However, if the author wanted to argue that, he would have said something about it in his argument. He didn't. If that is true, and it validates his argument, it's completely by coincidence.

The credited response, however, follows directly from his argument. We're making global warming happen faster. Why? Because grass is more efficient than trees. If that's your argument (and not something that I haven't stated but still believe and want you to magically assume), you have to be assuming that some of the grass is being replaced by trees. Only way the conclusion is possible with the premises I have.