Necessary Assumption Questions Help!

Pearson_Specter_Litt

Hi everyone! I have a question regarding necessary assumption questions. I am trying to get a better understanding of NA questions, since this is the area I am struggling with. I seem to be going for answers that seem relevant and may strengthen the argument, but are not needed/required.

For example, let's use this example from lsat trainer,

Argument: "Because we locked the door, no one can break into our house."

A possible correct answer choice may look like: "One cannot break into the house going through the chimney."

Wrong answer: "The door is the only way in and out of the house, and the locked door is impenetrable."

Here is a second example:

Argument: "My husband says I consume too much caffeine, but that is false. I only drink one cup of coffee a day, and one cup of coffee is not too much caffeine for a person to consume daily."

A possible correct answer choice: "She does not get an excess of caffeine from drinking tea."

Wrong answer choice: "Coffee is the only substance she consumes that contains caffeine."

The problem that I am having with these two examples from lsat trainer is that I am not seeing how the wrong answer is wrong. I understand for NA questions we are looking for an answer choice that is needed in order for the argument to be true. I did the negation test for the wrong answer choices and they still seem correct. For example in the second argument, the wrong answer choice is "coffee is the only substance she consumes that contains coffee" and in my mind when I did the negation test it was "it is not the case that coffee is the only substance she consumes that contains caffeine" or "coffee is not the only substance she consumes that contains caffeine." If that is true, couldn't this be an answer that is required for the argument?? If coffee is not the only substance she consumes that contains caffeine couldn't this wreck the argument??

Any help is appreciated! Thanks everyone!

Cant Get Right

NA’s closest cousin question is MBT. The only difference is the conditional aspect adds a step. So one foundational question that’s really important but that most people don’t know the answer to is: what is the sufficient in the NA question? You can’t have a necessary assumption by itself. It is defined by its relationship to a sufficient. So what is the sufficient which is defining the correct answer’s necessity? Do you know? Most LSAT students have no idea, but it is pretty foundational to grasping NA questions beyond a surface level of understanding. The answer is the validity of the argument, or, since the argument as given is always flawed, perhaps something more like the validity potential of the argument.

So with that in mind, I start NA by assuming the validity of the argument. By doing that, I’m mentally triggering the sufficient. With that done, it’s just a MBT question from there.

This also explains why the negation technique is logically sound. By negating the answer, we trigger the contrapositive and must negate the sufficient.

Argument: "Because we locked the door, no one can break into our house."

A possible correct answer choice may look like: "One cannot break into the house going through the chimney."

Wrong answer: "The door is the only way in and out of the house, and the locked door is impenetrable."

So start by assuming that locking this door is actually sufficient to conclude that no one can break in. The correct answer you seem to get, so why isn’t the wrong answer right? It certainly might be true. It would be consistent with the argument. Im pretty sure it would validate the argument. But remember, we’ve already validated the argument for the purposes of working the question. If that doors locked, no one is getting in. Period. So what if there is another door? What if it is also locked and impenetrable? If so, this answer is not true, but still no one can break into the house. So this answer doesn’t have to be true in order for this argument to be valid. It could be true. We just can’t say it’s definitely true based on the information we have.

Here is a second example:

Argument: "My husband says I consume too much caffeine, but that is false. I only drink one cup of coffee a day, and one cup of coffee is not too much caffeine for a person to consume daily."

A possible correct answer choice: "She does not get an excess of caffeine from drinking tea."

Wrong answer choice: "Coffee is the only substance she consumes that contains caffeine."

The issue here is, how much caffeine is too much? We know one cup of coffee is not too much, but is that the ceiling? Is two cups okay? Three? We don’t know. The correct answer accounts for that by referring to “an excess.” However much is too much, this deals with it. The wrong answer doesn’t. If four cups of coffee is the threshold for too much, she can drink a cup of coffee and three cups of tea (tea has less caffeine than coffee) and be fine. So again, the wrong answer may be true and would be consistent with and sufficient for that argument, but it doesn’t have to be true for the argument to hold.

Pearson_Specter_Litt

@"Cant Get Right" Thank you!! This is really helpful!!