Necessary Assumption | LSAT Logical Reasoning

Necessary Assumption questions in Logical Reasoning have correct answers that link together the chain of reasoning in the argument or defend the argument from something that would be devastating to the argument. This lesson looks at these relationships between the correct answer and the argument. It also covers the common reasoning structures found in Necessary Assumption questions and the trap answer patterns you need to know to be successful.
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[@fadingsmoke9206]

I dont think people like you get thanked enough. There are a lot of "teachers" out there but most of them dont really care. I know understanding is subjective and sometimes i dont get what you teach, but thank you still. So Much!!

[@grizzy161]

Thank you so much for ALL of these videos. You do an amazing job at breaking things down and explaining things, and better than anyone else i have seen on youtube. Every lesson makes me that much more confident! I am eternally grateful.

[@LSATLab]

Thanks for watching and for the feedback! That's music to a teacher's ears.

[@gtoor3798]

ugh fell for the mistaken reversal and then the too strong!! that is what I deserve for trying these at 1am... thank you for your videos!

[@ceceliadavis7845]

0000⁰⁰010

[@arthurisdope100]

I also fell for the too strong !!! Haha and it’s also 1am here Jesus I need to get good at these

[@babani8418]

me same😂

[@IGleeker]

I’ve been doing questions for the last 5 hours I feel you 🤣

[@westpalm124]

You guys have great content. My school unfortunately paid Blueprint $1,000. They are a joke, an absolute joke. They inject their lame opinions and references to pop culture and act like they are teaching 5 year olds with crayons and coloring books. I like how yall get straight to the point.

[@LSATLab]

haha, thanks for the kinds words, but you better not watch our RC videos, then (they involve cartoons). There are a lot of learning styles out there. Some people really need the jokes/distractions in order to tolerate studying. For others, it's a total inefficient use of time. Our mission (that we're still working towards) is to try to have enough resources that we can cater to different learning styles.

[@chenesaimoyo8983]

May we please have more

[@ahnafisBEAST]

Hey gotta say, these are quality videos. Thank you for that.

[@worldCitizen2011]

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[@worldCitizen2011]

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[@worldCitizen2011]

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[@worldCitizen2011]

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[@worldCitizen2011]

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[@Bolivia23]

Yes can we have more necessary assump and flaw videos!

[@chrisellely-portlandorreal9004]

Your videos are so good! Thank you!

[@B10Esteban]

Great lesson, thank you!

[@shanayaranashetty]

this is amazing! thank you for breaking it down so efficiently

[@yoyoyoyo7813]

indeed, this is very good video, thank so much

[@JehovahnieSaintRose]

BEST VIDEO EVER! THANK YOU SO MUCH!!

[@LSATLab]

Thank you!

[@alannaroman74]

Your videos are the best!

[@marlenmillan7819]

THANK U SO MUCH FOR THIS VIDEO!!!!

[@riyakapoor3218]

please make for analytical reasoning also

[@nicolewinn2927]

Thank you so much!!!!

[@sizz630]

Thank you so much for the lesson! I would like to ask the reason why the yellow part of the Healthy Back passage is the intermediate conclusion. I thought it was the main conclusion. I wasn't able to tell which one is the main conclusion even by asking myself "Why should I believe that?" question. I would really appreciate it if you could explain about it for me.

[@jakhongirabdurakhmonov7876]

A high level explanation. But knowledge is conjectural. I am still taking new insights even I watched this video two times thoroughly.

[@Nick-yg7ri]

Thank you for the video! One thing I'd like to know is, are there other indictors that tell us when we must defend vs linking the terms within the stimulus? Even in the defending question example I still found my self trying to link to terms instead of defending it. (reduction of class size -> education suffers)

[@LSATLab]

Great question. There are hints, but no guarantees. One hint in the stimulus that the correct answer will work by linking is when you see repeated terms and if/then statements. One hint in the answers that the right answer will work by linking is if/then statements. If you see negative language in an answer choice that's a signal that the answer works by a defending mechanism. Ultimately, there's no way to know for sure just be reading the argument whether the right answer will link the argument together or defend it from a dangerous idea.

[@getschwifty7413]

Thank you for the amazing videos and insight! Would you say these questions are comparable in difficulty to the real questions on the test?

[@LSATLab]

Yes, the questions in the video are real questions from the test. The first one, Q17 is representative of hard Nec Assump and the second one, Q13 is more representative of medium Nec Assump.

[@getschwifty7413]

@@LSATLab thank you so much!

[@jasonlou2013S]

Thanks!

[@Okiwan3]

I understand that the question stem for the linking example is prompting a necessary assumption question, but that linking question just seems so much like a sufficient assumption question to me. The whole building a bridge aspect just seems like we're looking for a sufficient assumption to reach the conclusion. Any tips on how to differential or conceptualize these differently beyond just the difference in question stems?

[@L3gion3r]

The question stem would place the correct answer choice in a sufficient position using a key word (same thing for necessary). It's just like a math equation. Example with a sufficient Qstem - "We have the conclusion, find X that leads to the conclusion" X > Conclusion. For Necessary it's reversed Conclusion > X . You can place them in the following visual relationship Sufficient Assumption > Conclusion , Conclusion > Necessary assumption. Learn your sufficient -necessary key words too: Sufficient: - If - , if… - When - Whenever - Every - All - Any - Each - In order to - People who - To be…. Necessary: - Then - Only - Only if - …if… - Must - Require - Unless - Except - Until - Without - If not

[@jmschmidt31]

I'm really struggling with the defending answer choice E. I would never pick E as an answer I would see it as completely out of scope. It's almost as if it's stating that the answer choice as a fact of the matter. The "teachers could not be persuaded to relocate in significant numbers to the educator's region". Could they not be? When was this introduced in the blurb or how does it apply as the ONLY assumption that can be made. I can't for the life of me see how this answer choice defends it from all criticisms. Maybe I'm just missing the point.

[@bethany6070]

When we solve necessary assumptions, we are looking for the answer choice that has to be true if the conclusion is true. A premise above tells us that there is a shortage of teachers in the region. So if we can't get qualified teachers from within the region, couldn't we just select some outside of the region to teach so that education wouldn't have to suffer? Answer Choice E is basically defining the conclusion to say "even outside qualified regional teachers aren't coming to teach" So, the conclusion regarding reduce class sizes -> education suffers still remains true if teachers are also not coming in from outside areas (answer E). I hope that helps.

[@maggimaloney6364]

Hi there! This is a very informative video but I wanted to let you know that your percentages on the trap answer portion add up to 105% instead of 100%.

[@LSATLab]

Thanks! The percentages typically don't add up to 100% because many answers are wrong for more than one reason. Though they should always sum to 100% or more.

[@abandonallhope.1040]

What if the stem asks which one of the following is required in order for the conclusion to be properly drawn? Is this necessary or sufficient style question?

[@LSATLab]

Hi Ashley, that's a Necessary Assumption question.

[@namanjain2995]

I thought the implication reverses in the healthy back question. The opposite side equally implies a healthy back and not the other way around. Can someone please clarify?

[@mr._sharpe]

This analysis makes your Comparative model for Neccessary Assumption look more conditional. I guess it overlaps...

[@LSATLab]

It does indeed...

[@yashraj8827]

Question: What is the difference between Linking framework of Necessary Assumption and Sufficient Assumption as their explanations to the approaches sounded very same?

[@LSATLab]

There isn't really a difference, in terms of picturing the Conclusion as the logic path we're trying to build, reviewing the evidence for what parts of that path have been given to us so far, and then predicting an answer based on what part of the path is still missing. The differences would only come at the answers. With Sufficient Assumption, we'll ask ourselves whether an answer, when combined with the evidence, allows us to mathematically derive the conclusion. With Nec Assump, we'll just ask ourselves whether the author clearly was thinking the way this answer accuses him of thinking. And we might subject the answer to the negation test: if negating the answer badly weakens the argument, it's correct. Another way to put that is SA can overdeliver on the link we're missing (be stronger than what we need) but it can't underdeliver (be weaker than what we need). Meanwhile, NA is the opposite. It can underdeliver (if you need $20, then it's still true to say you need $3), but it can't overdeliver.

[@yashraj8827]

@@LSATLab You're the first youtube teacher that I have tried to learn with, who is so responsive to the questions......this is I think the 3rd time you have actively replied to my question........thanks it cleared the doubt............Hope to learn many more from this channel.....

[@FurbiidN]

Alhamdulillah.

[@Bossanik]

Question is: How do you solve this in 1 minute?

[@LSATLab]

You dont always solve one of these in under a minute. Some should take as little as 30 seconds, some as much as 4 (maybe more) minutes. I saw a recent score report of someone who scored 178. The fastest question was answered in 29 seconds, the slowest in 6 minutes 18 seconds. That student didnt miss any questions in that LR section. The student’s pacing showed tremendous flexibility in how he/she approached LR questions. Early the section, dont use process, lean on intuition. Later in the section, go slower and take the time so you can use process when you get stuck. Go from street smarts early in the section to book smarts by the end.

[@Bossanik]

@@LSATLab Excellent response, thanks, this gives some hope!

[@yashraj8827]

Question: Is there any way by which we can distinguish linking assumption questions and defending assumption questions, or will it only come by practicing and experience?

[@LSATLab]

Unfortunately, you cannot know for sure which way the answer will work. But you can anticipate with a high degree of confidence. When you see terms repeating and some if/then logic you can anticipate with a high degree of confidence that the answer will link the chain together.

[@yashraj8827]

@@LSATLab I see......what u mean is mostly when we see conditionals, probability of question being of linking assumption is high? 🤔

[@LSATLab]

@@yashraj8827 Exactly. To be more precise you could add causal and comparative chains, but those are less frequent. A --> B --> C (conditional), A < B < C (comparative), and A cause B cause C (causal).

[@yashraj8827]

@@LSATLab Thanks for being responsive.......It certainly helped

[@yashraj8827]

Question: On the linking assumption practice question my approach was like this: Healthy back------->Balanced muscle development And, Proper Alignment------>Opposite Muscles Equally These were premises and here if we connected "Balanced Muscle Development" to "Proper Alignment", won't we reach to our desired conclusion. Healthy back-------> Opposite Muscles Equally And that lead me to "A". Where was I wrong?

[@LSATLab]

That all makes sense to me. Conversationally, we'd think "She's assuming that balanced muscles require proper alignment". Conditionally, (A) would look the same, but it's switching from requirement language to guarantee language. Conditional logic doesn't show us which idea (the trigger or the consequence) occurred first chronologically. But if we're saying that "balanced muscle development REQUIRES proper alignment", then it sounds like proper alignment comes first. It is the underlying condition that allows for balanced muscle development. (A) is making it sound like balanced muscle development comes first and causes proper alignment. There is a Cause/Effect logic to "will be enough to *keep* the back in proper alignment". If you negate (A), and say that balanced muscles are not enough on their own to achieve proper alignment, that wouldn't conflict with what the author is saying. The author just thinks that balanced muscles REQUIRE proper alignment. She never said that balanced muscles on their own make proper alignment happen.

[@SidMera]

Appearing for LSAT June?

[@yashraj8827]

@@SidMera Naah........just expanding my horizon while preparing for clat.....

[@SidMera]

@@yashraj8827 oh ic

[@ashleychase7501]

In the second question, why is it okay to translate "probably not improve student achievement" with "education suffers" in the conditional statement?

[@LSATLab]

haha, you're totally right. (This is my first time seeing that part of the video; this is Patrick, not Matt) Saying "probably won't improve" is definitely not equivalent to "education will suffer". What he's doing there, but he doesn't explain what he's doing, is "playing along" with the intended match of Conclusion language and Evidence language. We know that both the conclusion and the evidence are talking about "reducing class size". Since the conclusion is expressing some negativity towards the effect of reducing class size on student achievement, there must be some sort of negativity in the evidence to match up with that. And the phrase in the evidence that sounds negative about student achievement is "education "suffers". So Matt is being charitable to the intended match. He's trying to illustrate how the argument would work on a symbolic level in that part of the video, so he's deliberately "playing along" with the gist of the argument so that he can use one consistent symbol to refer to both "education suffers" and "not improve achievement". It's also relevant that the EVIDENCE says something harsher than the CONCLUSION. If we establish that X causes education to suffer, then it's perfectly fair to say X will probably not improve student achievement, because that latter claim is softer than the evidence for it. It would cause an objection in us if the author had established that "X will probably not improve student achievement" and then concluded that "X will cause education to suffer". That would be an unfair move we would surely resist.

[@bara2636]

i still don't get the difference between sufficient and necessary assumption, seems like both using the bridging gap notion

[@LSATLab]

In many cases (an argument with only one missing link), they will feel the same. But an argument with multiple missing links wouldn't be eligible for a Sufficient Assumption (because establishing one of those multiple missing links wouldn't prove the conclusion). For example, "Dennis is really good at ping pong. Thus some janitors are fantastic athletes." We have two missing links there. We're assuming "Dennis is a janitor" and "being really good at ping pong means you're a fantastic athlete". Each of those NEEDS to be assumed, but neither of those on its own would be SUFFICIENT to prove the conclusion. The other way in which NA will be very different from SA is that around 40% of correct answers on NA have nothing to do with bridging a gap. They are instead Ruling Out an Objection (we call those DEFENDER style). For example, "Dennis applied to USC. Thus, Dennis must want to go to a great school." This argument, too, has multiple missing links: - "USC is a great school" - "applying somewhere means you want to go there" But you can write a million different NA's for this that would rule out an objection. All of these would be a correct answer on NA: (A) Dennis was not forced to apply to USC by his grandma. (A) Dennis did not just apply to USC to see whether he could get in (A) Aliens did not temporarily take control of Dennis's body and fill out the USC application form for him. All of those need to be assumed. None of them would prove the conclusion (none would be a sufficient assumption). A lot of us have the same reaction when we first are learning about NA vs. SA. You just have to experience a wider variety of questions to start better internalizing the diff. Ultimately the tasks are diff: SA: which answer, if true, proves the conclusion NA: which answer, if negated, most weakens the argument

[@yalelaw]

1:34 is a sufficient assumption question bruh

[@LSATLab]

nope, not according to the LSAT

[@LSATLab]

I should have included in my response that "only if" indicates a necessary assumption, while had it only stated "if" it would have been a sufficient assumption.

[@victorugwuanyi7403]

Hi I have a question

[@LSATLab]

What is it?

[@ashleychase7501]

Why doesn't A work?, if healthy back -> balanced muscles balanced muscles -> proper alignment proper alignment -> opp. sides equally doesn't that mean healthy back -> opp. sides equally?

[@LSATLab]

It does. What you just wrote, "Healthy back --> opp sides equally" can be read "IF healthy back, THEN exercised opposite sides equally" or it can be read, "Having a healthy back REQUIRES exercising opposite sides equally". Any conditional, X --> Y, can be read a variety of ways: if X, then Y all X's are Y X guarantees Y but the most important variation is X requires Y As you wrote, "in order to have a healthy back, it's required that we exercise opposite sides equally". I might equivalently say, "In order to get into Yale, it's required that you have a decent GPA." But it's a very different meaning when we switch from saying something is REQUIRED to saying it's SUFFICIENT. (A) says that "exercising opposite sides equally WILL BE ENOUGH to guarantee proper alignment". We certainly wouldn't say, "having a decent GPA will be enough to get you into Yale". (A) is taking a conditional relationship we have in the stimulus and just reversing it. "Opp sides equally --> Proper Alignment" More conversationally, that last sentence is saying that "to keep the back in proper alignment, you must exercise both sides equally". But that doesn't mean that's ALL you have to do. Maybe it's also true that "to keep the back in proper alignment, you need to sleep on a firm mattress." Hence, the author could say, "Exercising opposite sides equally will NOT be enough to get your back in proper alignment. You also need to sleep on a firm mattress ... sit in a well-postured office chair, etc." Let me know if any of that was confusing.

[@justinaknight8495]

Okay so what is the main conclusion. I don’t need the intermediate conclusion

[@jgadonisspeaks]

These questions were both awful and neither really hits what needs to be hit in order to fully understand this question type. I’ve yet to come across anyone to explain it plainly and show it applied.

[@LSATLab]

Thanks for your feedback. Super helpful :)