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Related Discussions
Necessary Assumption help
wonsuh1076
Member
Hello, I have been struggling with necessary assumptions for a surprisingly unnecessary amount of time and still I cannot totally understand the concept as I have received seemingly conflicting methods to solve this question stem. Let me start with a simple question: if You negate a statement, and that statement makes the conclusion MUST BE FALSE, then that statement before its negated is the necessary assumption? If a statement is negated and the conclusion is COULD BE FALSE, then the statement before it was negated has no bearing on the argument and is not a necessary assumption? I really need help strengthening my firm understanding of this concept because it has been hit or miss for me. I sometimes would get most of them right in a PT and get most of them wrong in another PT, 50-50 right in another PT. Please help
Comments
That's not quite it. A necessary assumption, if negated, would wreck the argument. A necessary assumption is something that, if negated, would make it such that the premises do not support the conclusion. The conclusion itself could still be true with a negated necessary assumption.
Necessary assumption questions ask us to determine what has to be true. The necessary assumption is never explicitly stated, but we have to "fill in the gap” and bridge the premises to the conclusion (with an answer choice that has to be TRUE and which is the necessary assumption) in order for an argument to work.
If a necessary assumption (an answer choice) were discovered to be false (by negating), the argument would fall apart and the conclusion would not follow logically from its premises and that would give you the correct answer choice, so yes, you are correct in your first question.
When negating the truth of an answer choice, if negating causes the argument to be strengthened or to be unaffected, then that answer choice is incorrect.
A necessary assumption is what has to be true, for the argument to follow.
Steps for Necessary Assumption:
1. Identify and the conclusion in the stimulus and identify the premises.
2. Accept the conclusion as stated.
3. Find a necessary assumption (an answer choice) that makes that stimulus argument follow logically from its premises and the conclusion.
You have to bridge those premises (including your answer choice which has to be the necessary assumption) to the conclusion, further showing that with the answer choice (necessary assumption) you choose, proves that conclusion is true.
I hope this post helps.
Be careful not to confuse necessary assumptions for sufficient assumptions. Necessary assumptions do not have to logically guarantee or "prove" the conclusion. A necessary assumption merely keeps the argument afloat (i.e. the necessary assumption being true gives the argument a chance at being valid).
A sufficient assumption is an answer choice that makes the argument valid by, in conjunction with the existing premises, logically guaranteeing the conclusion. Some necessary assumptions are sufficient assumptions, but this is not always (and in fact usually is not) the case.
Consider an example where we want to prove that X is a good basketball player. "X is LeBron James" is a sufficient assumption, but that obviously is not necessary to show that X is good. However "X can hold a basketball" is a necessary assumption, because, without it, X has no chance of being a good basketball player. And, surely, that X can hold a basketball does not guarantee that X is a good basketball player.
Not confusing the Necessary vs Sufficient assumption.
The Sufficient assumption proves the conclusion 100% true, the conclusion proves the Necessary Assumption.
so the premise does not have to make the conclusion impossible for a negation to wreck the argument? It just has to at least make the existence of a premise cause a person to have a "so what" expression" in regards to the strength of support to conclusion?
The correct answer choice must be true for the argument. When reading the stimulus, you have to assume that the argument is good, which means the premises are sufficient for the conclusion. Based on this, when you are reading the answer choices, ask yourself is it MBT? If it is not true, the premises aren't sufficient for the conclusion anymore.
When negating an answer choice, we aren’t trying to wreck the conclusion, we are trying to wreck the argument and render the argument invalid. Negating an answer choice is finding the logical opposite. For example “All people are running a marathon” would be in logical negation terms “It is not the case, that all people are running a marathon," which further means Not all people are running a marathon and Some people are not running a marathon. If you do negate one of the answer choices, and if that negated answer is the correct answer, it will wreck the argument if it is the necessary assumption.
A necessary assumption (the correct answer choice) must be true in order for an argument’s conclusion to be properly inferred. The correct answer for a necessary assumption is something that must be true for argument to be valid, however it does not have to guarantee that it will happen and that is why common correct necessary assumption questions have weaker answer choices.
For example, consider this argument:
Jack and Bill are running a marathon. Bill is the faster runner. Therefore, Bill will win the race.
Example answer choices for necessary assumption.
The faster runner sometimes wins the marathon.
Bill will not break his ankles during the marathon.
The marathon will actually happen.
If we negate the above. All of these three negated choices wreck the above argument.
“It is not the case that the faster runner sometimes wins the marathon”
“It is not the case that Bill will not break his ankles during the marathon”
“It is not the case that the marathon will actually happen”
You will find correct answer choices where the correct answer choice for the above Necessary assumption question is something that must be true for Bill to win the marathon, but it does not have to guarantee that Bill will win.
Find an assumption that must be true in order for the conclusion to be properly inferred.
When you negate an answer choice, the correct answer invalidates the argument.
The conclusion is what proves the necessary assumption.
https://7sage.com/lesson/how-to-approach-necessary-assumption-questions/
It seems as if that based on the premises, the negation of the example answer choices make it impossible to draw out a conclusion from the premises. If it is never the case that the faster runner wins the marathon or the case that Bill will break his ankles in the marathon, it seems that based on the premises, the conclusion just cannot reasonably be true. If it is never the case the faster runner wins the marathon or the case that Bill will break his ankles in the marathon, how can you win the marathon in the first place? I understand that the conclusion in it of itself can be true, but based on the premises given and the negation of the example answer choices given, the conclusion just seem to be impossible. On the last negation where you state the marathon will actually not happen, that seems to completely make the premises that Jack and Bill are running the marathon invalid and the conclusion that Bill will win the race impossible. These negations make it seem as if something makes it the premises invalid, or the conclusion invalid, or the conclusion invalid based on the premises given. And I do agree that the negation of these example answer choices wreck the argument. But like on question 16 of LSAT 28 section 3, where the correct answer is some people in Beethoven's time did not ingest mercury, if we negate that then that answer is everyone ingested mercury. I understand that this negation based on the premises that mercury was commonly ingested in Beethoven's time to treat venereal disease, makes that premise do nothing for the conclusion that if researchers find a trace of mercury in his hair, veneral disease did not cause his deafness. But the negation of the answer choice that everyone ingested mercury in Beethoven's time does not seem to contradict the premise or the conclusion. It could still be true that the premises that mercury was commonly ingested in Beethoven's time to treat veneral disease and the conclusion that if researchers find a trace of mercury in his hair, veneral disease did not cause his deafness. So to put it simply, if I were to negate an answer choice which makes the premise does nothing for the conclusion, despite the fact that the premise or the conclusion may or may not be true, then that negation is destroying the argument?
When we negate that answer to “it is not the case the some people did not ingest mercury” then the argument including the conclusion gets recked because we can’t conclude that the hypothesis is correct. If everyone is ingesting mercury, how would one be able to tell the difference from his hair and anyone else’s hair if everyone was ingesting mercury? 16 of LSAT 28 section Is a tough question and one of the more complicated. I try to switch from negating if I have to, while also at times having the conclusion prove the necessary assumption true.
Consider PrepTest 34 - Section 3 - Question 03
The premises:
P1 Sigatoka disease drastically reduces the yield of banana trees and is epidemic throughout the areas of the world where bananas are grown.
P2 The fungus that causes the disease can be controlled with fungicides, but the fungicides can pose a health hazard to people living nearby.
P3 The fungicides are thus unsuitable for small banana groves in populated areas.
P4 Fortunately, most large banana plantations are in locations so isolated that fungicides can be used safer there.
Conclusion:
Therefore, most of the world’s banana crop is not seriously threatened by Sigatoka disease.
We need to find a bridge that allows the valid argument with a necessary assumption.
My understanding is...
If we negate answer choice B with “It is not the case that Large plantations produce most or all of the world’s bananas” then that wrecks the argument including the conclusion because it is not valid to say that with the premises 2,3, & 4 and with the conclusion; "Therefore, most of the world’s banana crop is not seriously threatened by Sigatoka disease,” proves the argument is invalid because premise 3 told us that the fungicides are thus unsuitable for small banana groves in populated areas and Premise 4 says fortunately, most large banana plantations are in locations so isolated that fungicides can be used safer there, then this argument gets wrecked because we negated the necessary assumption and therefore "if it is not the case that Large plantations produce most or all of the world’s bananas" means that small banana plantations could be most or all of the producers of bananas, therefore wrecks the argument. If you wreck an argument you are wrecking the premise(s) and conclusion(s) and making the argument invalid.
an argument = Premise(s)+Conclusion(s)
i think I understand now thank you. In one of the negations you posted for the marathon example, "It is not the case the faster runner sometimes wins the marathon". If however one of the answer choices was The faster runner wins the marathon, the negation of that would not destroy the argument right? The negation of that statement would be The faster runner sometimes does not win the marathon?
Jack and Bill are running a marathon. Bill is the faster runner. Therefore, Bill will win the race.
The faster runner wins the marathon negated to “it is not the case, that the faster runner wins the marathon seems like it would wreck the argument, but that seems like it is too much of a strong answer choice for a necessary assumption, but could be an answer choice depending on the other answer choices. We would likely see an answer that says,“the faster runner, sometimes, wins the race." The correct answer choice for the Necessary Assumption question type is an answer choice that must be true, but does not have to be guaranteed. For the marathon question, for Bill to win the race we would find an answer choice that must be true, but certainly does not have to guarantee that Bill will win the race.
I hope I didn’t confuse you. It helps me to try and explain information, and I hope I helped. Reach out and direct message me, if you need more help.