Must Be True | LSAT Logical Reasoning

[@harshithamarathe6792]

I love how you break down the arguments and show the relationships between statements so well. I’m preparing for GMAT but this was probably the clearest way someone has explained arguments. Thank you so much!

[@taylor07132]

Thank you for taking the time to make and upload this video and all the other videos in this series! I have found them very helpful! You are a blessing!

[@isaiahkim8423]

I've always wanted to know the types of reasoning methods and their frequencies in a question type. Your contents are very useful to prepare how to approach each reasoning structure. Thank you!

[@L3gion3r]

Thanks dude! Hope that your recovered from that cold.

[@dianachang7182]

Very good explanation! I have been struggling with this type of LR question.

[@Reese8036]

Thank you so much! 7Sage goes to mechanically on these types of questions.

[@ВиталийОвчаренко-т7й]

In the context of LSAT Logical Reasoning, the phrase "Must Be True" refers to statements that are necessarily accurate and supported by the given information or arguments within a particular question or passage. These statements can be deduced logically from the premises provided, and they represent the core conclusions that one can draw based on the available evidence. In order to identify "Must Be True" statements in LSAT Logical Reasoning questions, you should carefully analyze the provided information and arguments, and look for the most reasonable and well-supported conclusions that can be derived from them. This often involves understanding the relationships between different pieces of information, recognizing logical fallacies or inconsistencies, and considering the context in which the statements are made. To excel in LSAT Logical Reasoning, it is essential to practice identifying "Must Be True" statements and strengthen your critical thinking and logical reasoning skills. This will help you not only in answering LSAT questions accurately but also in developing a strong foundation for legal reasoning and analysis in your future law studies and career.

[@Shawn6751]

Thanks for the videos, these videos are saving my rear end.

[@taylorneu5532]

How does the relationships imply the reverse at 11:23 prove the inverse is wrong? I don't follow the logic of "if you reverse it its not true". Wouldn't you be able to invert both sales decrease into sales increase creating rising profits, and only selling coffee into increased products with the statements you've listed?

[@SheltonTammy]

This is much appreciated. Thank you.

[@ravisandhu9010]

At 23:40 you state that you cannot negate in the forward direction. However, in the causation video, Patrick stated that no cause, no effect or less cause, less effect is a correct answer choice in causation-based reasoning questions. Is there a difference between these two ideas?

[@LSATLab]

Hey Ravi, there sure is. Context matters. No cause and no effect would strengthen a conclusion that put forward a causal relationship. It would not prove the relationship, but it would make it more likely to be true. In this case, we're talking about a conditional relationship and we're on a Must Be True question. In the latter, we need to find something that must be true. In the former case, we're looking to add support to the conclusion. So you have two big differences. Your task is different (Must Be True vs. Strengthen) and the reasoning structure is different (Conditional Logic vs. Causation).

[@ravisandhu9010]

@@LSATLab I apologize for asking this, and I appreciate your response immensely. However at 19:21, the video states this question falls under the causation reasoning structure based Must Be True questions. Based on your guidance in the Conditional Reasoning video, I completely agree that if this Must Be True question utilized conditional logic, it would not be permissible to do a forward negation. However, this question uses a causal chain with causation based reasoning as indicated by the language. Thus, is there a difference between what must be true in a causal chain and what can be added to strengthen a causation-based conclusion (no cause, no effect)?

[@matenina3906]

When taking the timed lsat do you recommend diagramming each question with the causal/conditional relationships? If not how do you keep track in your head especially on virtual tests?

[@devinhawkinson7975]

7:00 Can't you follow assume if P than not M then not K thus L. Therefor getting you both P implies L and P implies not L. Does this contradiction matter?

[@MorganHorse]

Listening to the first example has me feeling like such an idiot lol. If this premise is applied to something, I’m very good at these questions through context. But with this, I’m struggling to follow. That said, I’m multitasking. Maybe I’ll come back to say I figured it out. How I know that P is not L just because P is not M without the nuance of what they actually are? Edit: yep I got the first applied question right lol. I just don’t like making assumptions.

[@francescacolby6513]

How is D for the last question negation. To me it seems to be reversal and negation.

[@oliverupload]

Interesting but I don't believe this is correct (18:55). Why is B) "too strong" when the statement is literally word for word in the paragraph: "Danaxil - stops pain more quickly." If we are taking the advertisement at face value this is exactly what it's saying. In mathematical terms that would indicate Danaxil headache time < competitor head ache time which is answer B). The answer choice of C) in mathematical terms would indicate Danaxil head ache time

[@LSATLab]

Hey-hey. The statement in the stimulus doesn't say "Danaxil stops pain more quickly than other pills". It says "no pill stops pain more quickly". Say there were 10 runners in a mile long race. Joe and Mike both crossed the finish line at the exact same time (4 mins, 0 secs). They tied for first place. We can say "No runner ran more quickly than Joe". We're not denying Mike the tie by saying that. It's also true to say "No runner ran more quickly than Mike". That's the same verbal shenanigan they're playing here. We know that all other competitors ≤ Danaxil, not that all other competitors < Danaxil. Let me know if that doesn't make sense.

[@tvitas]

I feel that I have to agree with you on this as well. I read the response below, but it still doesn't make sense to me. I understand the verbal shenanigan in the runner example, but correlating it to the question in the video doesn't add up. "No pill stops pain more quickly" = no competitor stops pain more quickly. I would also have gone with choice B on this one. The whole explanation about the 20min reference I would see as assumptions. Going off by the advertisement, it does not state anything to imply a competitor can relieve headaches at the same time as Danaxil. I want to believe the answer is C, but i'm not grasping it lol..

[@KKSportsKKS]

@@tvitasthe advertisement states “No headache pill stops pain more quickly.” Never does it say Danaxil is quicker than any other pill, that is a false assumption. The advertisement only guarantees nobody else will be quicker. The original comment was blatantly incorrect in restating the passage, and contradicted themself towards the end. Despite that, their

[@francescacolby6513]

What if conditional statements don’t link. What do u do then?

[@devanshisharma2580]

18:27 v well explained!

[@GopiRamanathanLSAT]

@LSATLab How are "must be true" and "could be true" questions different from one another? Do the tactics change in any significant manner between those two varieties of question, or would the approaches mostly be the same? I'm assuming you may have a video on this but I'm not sure which one it is haha

[@LSATLab]

There aren't any "Could Be True" questions in Logical Reasoning (you might be thinking of Logic Games, where those are common). On *Must Be False* questions in Logical Reasoning, the four wrong answers each could be true, but we don't actually have a way to prove something could be true. We just consider that it could be true if it's not contradicted by the statements.

[@Bossanik]

What's the difference between Casual and Conditionals, these two are often easy to confuse, can you do some videos in this subject?

[@LSATLab]

We do have a video called "Causation" and a video called "Conditional Logic". "Causation" is much more likely to help you with GMAT CR, since Assumption / Strengthen / Weaken / Evaluate questions often feature an author concluding a possible explanation for a curious fact (and GMAT primarily likes to test alternate explanations). Conditional Logic isn't really going to help you on GMAT. It essentially never shows up. There will be an occasional Inference (aka Draw a Conclusion) question that will involve a rule, which *could* be expressed conditionally, but you're never chaining conditionals together or dealing with particularly tricky conditional trigger wording. So you'd be fine handling that rare Inference question without ever diagramming a conditional statement.

[@Bossanik]

@@LSATLab Really appreciate the feedback, also the videos are one of the best prep videos that are out there, very organized and methodological, are you guys also tutor for GMAT? If so, what's the contact? Thanks! I master GMAT RC by stating with LSAT RC, I kept going on with LSAT until I hit 90% RC accuracy, now I don't usually get any RC wrong unless they are 4 or 5 difficulty, at which level my accuracy ranges from 50-70% max, so I thought I would start with LSAT for CR as well to build a base. I am reading Ellen Cassidy's The Loophole in LSAT, it's an user friendly book but I found some of the concept are counterintuitive, I also have PowerScore GMAT CR, which I plan to read next, do you think following your video playlist will help? If so, what are the ones I should focus on, I am not sure which ones are in particularly tested more frequent in GMAT, in comparison to LSAT, Sorry for such a big reply, appreciate you making these videos available to public, helps general students who cannot afford quality material or tutor, thanks again!

[@LSATLab]

@@Bossanik , we aren't a GMAT company yet, but we will probably expand in a year or so to other test types. The useful for GMAT videos would be any of the Reading Comp videos (right now there are just big picture reading videos up, and those are relatively the same as GMAT reading advice ... the forthcoming videos that break down question types will all be applicable). For CR, you might wanna do Strengthen, Weaken, Evaluate, Assumption, Paradox (Explain Discrepancy), Comparisons, Causality, and Most Supported. Role might help a bit (for those boldface questions), but LSAT gets more into argument terminology than GMAT. I haven't read Loophole, but I've heard good things about it. There will definitely be a lot of stuff in there that isn't super relevant to GMAT CR (famous flaw stuff like Part vs. Whole, Nec vs. Suff, Circular, etc. is not relevant). And stuff relating to conditional logic is not relevant. Also Parallel Reasoning questions are incredibly rare on GMAT. But I think/hope she teaches a rebuttal style of analyzing arguments ... something like, "GIVEN this evidence, HOW CAN I STILL AVOID BELIEVING the conclusion (or how can I argue the opposite of the conclusion" That mentality is definitely worth rehearsing for CR arguments.

[@Bossanik]

@@LSATLab Thanks a lot once again for taking the time, looking forward to the RC videos!

[@blingbling2309]

that second question is trifling as fuck

[@Bossanik]

It's fucked up!

[@SidMera]

Indeed😂

[@zenobiasarkari4836]

very helpful, thank you so much!!

[@Mayelinida]

I don't really understand the reversal thing. Is option C technically not a reversal of the argument also?

[@LSATLab]

Which part of the video are you asking about? Choice (C) on which of the questions? Are you talking about the one with coffee prices?

[@Mayelinida]

@@LSATLab Yes 🥺

[@LSATLab]

@@Mayelinida No, C isn't a reversal. You might be getting confused based on the fact that the "if" is placed deep into the sentence, rather than at the beginning. There's no difference between saying "if X happens, Y happens" and saying "Y happens if X happens" Both of them would be diagrammed X --> Y Wherever in a sentence the "if-condition" appears doesn't matter; it belongs on the left side of the arrow. (C) said, "The shop's profitability will decrease if the price of beans increases", so that would look like "Price of beans increase --> profitability decrease" And as Matt walks through there, we know that 1. if price of beans increase, then shop's prices will increase. 2. if shop's prices increase, then they'll start selling noncoffee stuff or sell less coffee" 3. in either case, that leads to decreasing profitability (we are separately told that selling noncoffee leads to decreased profitability, and told that selling less coffee also leads to decreased profitability). So it's true that if the price of beans increase, then the profitability will decrease, as (C) says. Let me know if any of that was confusing.

[@malihaahmed8434]

I'm still having a bit of trouble understanding why D is incorrect for the last question. Could a potential reason be because we cannot conclude that algae will not proliferate in estuaries that are not polluted. There could be another cause that makes them proliferate?

[@malihaahmed8434]

Thank you for the videos! They are very helpful :)

[@noahslinker8185]

Yes, you're correct at the end there. Think of it in terms of the sufficient and necessary conditions - if there is sewage (sufficient), then there is algae (necessary). Contrapositive being if there is not algae (sufficient), then there is not sewage (necessary). What answer choice D does is negate without fully committing to the contrapositive (flipping the sufficient and necessary when making a negation) - this being if not sewage (sufficient), then not algae (necessary). Do you see the error there compared to the correct contrapositive above? In plain English terms, there's nothing in the stimulus that says sewage is the *ONLY* cause of algae in the estuary, but that sewage *WILL* cause algae if present. There could be other factors that cause algae without sewage present, there might not be - it's just not stated. I think you could argue that D is incorrect also because it's unsupported by the stimulus. The LSAT is very rigorous with the language used and what words specifically mean. Unfortunately, those meanings are often different than what our colloquial understanding is. I hope this helped out!

[@robertbusk1977]

I will die on the hill that these are the hardest LR questions

[@kj62175]

🔥🔥

[@Mayelinida]

But doesn’t the wording matter? I thought about that when looking at option A but then I thought it says K or L and not K and L… Please can you explain

[@LSATLab]

Hey, I'm not sure I understand your question. When there is an "or" in the trigger, then either trigger idea is enough on its own to guarantee the outcome. For example: "If I watch a sad movie or if I read about climate change, I get sad". We could separate those into two rules, if we wanted to: "watch sad movie --> sad" and "read about climate change --> sad" So the rule, "If K or L, then M" could be broken up into K --> M and L ---> M Whenever K is true, M is true. Whenever L is true, M is true. If K and L both happen to be true, M is true. If there were an "and" in the trigger, then you can't split them up into their own rules. For example, if the rule said "If K and L, then M" then knowing that K is true wouldn't be enough to tell us that M is true. We would still need to know whether L is true before we could guarantee that M is true. Is that what you were asking about?

[@anirbanmukherjee5240]

(1) K or L -> M. (2) NOT K -> L. Taking the contra positive of 1, NOT M -> NOT K AND NOT L. But NOT K -> L (as given in 2). Contradiction in the setup?

[@LSATLab]

Great observation! It's not quite a contradiction, but there is the potential FOR a contradiction. If M were out, a contradiction would ensue. So one of the things you can infer from those three rules is that M must be in. (I'm using in/out as a proxy for yes/no, but same difference) Another way to think of the same thing is that the last rule looks like this: ~ K --> L ~L --> K That guarantees that at least one of L and K is in. They can't both be out, because either one being out would force the other one in. So since we know that at least one of L and K is in, we know that the trigger of the first rule is going to happen no matter what, and thus we know that M will be IN no matter what.

[@anirbanmukherjee5240]

Yep. That makes sense. Thanks!

[@Jonathanfootball144]

Make more

[@LSATLab]

More coming as quickly as possible :)

[@chenesaimoyo8983]

We really need more , so helpful

[@chenesaimoyo8983]

@@LSATLab thanks please do

[@mailinho1683]

Thank u

[@riyakapoor3218]

very useful

[@mdimtesal]

Hey, are you appearing for LSAT 2020?

[@Bossanik]

Hit like if you are doing this exercise as a part of your GMAT prep!

[@pamelabrigtte]

I stopped diagraming LR questions.

[@francescacolby6513]

I hate these questions. They have cause me so many breakdowns. I’ve watched and read everything and done so many practice questions and test and still don’t understand it. Does that mean I just can’t understand them ever? I’m losing hope.

[@otstent985]

No bro go to lsat demon , you will get better

[@francescacolby6513]

@@otstent985what happen about LSATMax ?

[@KiplingGeorgia-e6p]

Robinson Betty Walker Sandra Davis Barbara

[@ridhimaraj6115]

Plz Make videos in hindi language

[@LSATLab]

One day, I'm sure we will. Thank you for the suggestion Ridhima!