[Music] you hi this is Patrick from LSAT lab we're here to talk about must be false questions in the logical reasoning section these guys are pretty rare only about 1% of questions so on most tests we don't see any of these and when we do see them typically it would only be one per test we want to talk about how to spot one how we should think about reading it and breaking it down what sort of reasoning structures are likely or unlikely to show up and what sort of trap answers we might look out for here are a few examples of a must be false question stem which of the following must be false keywords too obvious which can not be true if the statements above are true that tells you you're doing some sort of inference question because they're calling the paragraphs statements rather than an argument or reasoning and instead of asking us what must be true or what's most supported as a typical inference question would this actually says which can't be true this one feels a little bit more like logic games where we are often asked each of the following could be true except and we know to convert that into four of them could be true one of them must be false there's a softer version of this that's sort of like the difference between must be true and most supported instead of flat out saying must be false they'll just say it's the least compatible but when LSAT uses the term incompatible or incoherent it means contradictory so the least compatible means the most contradictory again this question stem is referring to the paragraph as statements which tells us will be reading facts and information not an argument when we're in the inference family we're not reading arguments so we're really reading facts and seeing if they have any relation to each other particularly we look out for conditional and causal relationships we look for overlapping ideas if something's being brought up more than once then usually we can derive something by combining the two facts were given about a certain thing if we are reading and we see conditional logic wording will definitely start thinking about maybe diagramming some of the conditional logic if we see comparative or causal wording which is much less rare here that we might enter more of that sort of mindset seeing if there's a causal chain we're trying to sort of itemize where are their similarities where are their differences between these things being compared when it comes to step 3 anticipating an answer there are two main directions that you you will usually see a correct answer go on it must be false it'll typically either contradict a conditional statement that we were given or it'll contradict a possible inference that we could have made let's look at each of those so let's say that Solomon is a polite eater he only double dips his shrimp when the cocktail sauce is down to its last bits and he often uses a wet-nap after he's done if we were being asked which of these must be false could it be true that using a wet-nap is considered impolite kind of tempting I mean we said Solomon was polite we said Solomon uses a wet-nap so this feels like it's going against that it's saying using a wet-nap impolite however it never connected politeness to using a wet-nap both of those things were mentioned but it never said if you're a polite eater you always use a wet napkin after you're done eating something messy so this does not contradict anything beast says that he always uses a wet nap before he eats and we might think cool we don't know that you know we only heard that he uses it after he's done eating okay this is wrong but is it contradicting anything the danger on must be false is that we confuse something that we wouldn't be able to prove with something that is provably false so we don't have any idea maybe he uses a wet map before he eats and after heats and throughout he goes through a lot of wet naps when he sits down to eat shrimp all of that is compatible with the passage see says that at his birthday party he took a fresh bowl of cocktail sauce out of the fridge and dipped his shrimp in it twice it seems like a relatively innocuous idea but wait we were given a rule that says he only double dips if it's down to the final bits and this is a fresh bowl so this actually does contradict something we were told we were told a conditional signified by the word only when only and only if and only when always indicate necessary conditions so this is actually telling us that in order for him to double dip his shrimp it's a requirement that the cocktail sauce is down to its last bits required things go on the right that's called the necessary condition that required the necessary thing the contrapositive would say if the sauce isn't down to its last bits he's not going to double dip his shrimp but we were just given a counter example when you're trying to contradict a conditional it has nothing to do with negating or contra posing it just means provide one counter example the form of a counterexample is always something in which the trigger happens but the outcome doesn't so in this case he double dips but it was not the case that the sauce was nearly done the C would be the correct answer here it contradicts a conditional one of the ways in which they make that answer less obvious and less appealing is by putting in extra details like birthday party or his fridge if we see a conditional in the statements we should pay a lot of attention to it because it's very likely that a correct answer will do this say that the trigger happens but say that the outcome isn't happening the other type of correct answer on a must be false question is an answer that contradicts something that we could have inferred from the statements by pulling two or more facts together if we look at these statements Solomon has been trying to cut down on his shrimp eating for the past two weeks the number of shrimp he's been eating has indeed declined although the total weight of shrimp he's eating has not and every day he writes another blog article about freeing himself from the tyranny of shrimp if it wasn't already obvious these are not very realistic LSAT paragraphs so if we're being asked here which of the following must be false pause the recording and take a look at these three answers and then unpause when you want to hear about them welcome back is it possible that no one including Solomon reads his blog it is all we know is that every day he writes another article we don't know if he reads that article we don't know if anybody else reads that article so it is possible that he is just typing these and no one is ever reading them hey could be true B says that the shrimp he was eating a month ago are heavier than the shrimp he's eating now well that actually is contradicting something we know there was a comparative relationship there that the number of shrimp has gone down but the total weight of shrimp has not gone down if we think about the math involved your total weight of shrimp is just how many shrimp you ate times the average weight per shrimp if I eat ten shrimp and on average they each weigh about 20 grams and I ate 200 grams of shrimp if we find out that he's eating the same total weight or at least as much even though the number of shrimp has gone down and the only way to balance out that math is to infer that the average weight per shrimp has gone up the possible inference these facts allowed us to make are that for the past two weeks he's been eating on average heavier shrimp B contradicts that idea and says that the shrimp he was eating a month ago are heavier than the shrimp he's eating now now there are slight technicalities with a month ago in the sense that our paragraph never exactly clarified what Solomon is doing a month ago but we will take this as a 98% provably false type answer see says that he only writes blog articles about shrimp can we infer that heavens no we know he writes blog articles about shrimp but he might write blog articles about other things as well I've heard he as a passion for wet-naps so see could be true could be false the important thing is it doesn't contradict anything in order for us to pick C we would have to be able to tell from this paragraph that he writes blog articles about things other than shrimp and we haven't heard anything like that so we have no way to contradict him so B was our correct answer it contradicted a mathematical inference we could pull out of that comparison again that two patterns for correct answers are that they will contradict a conditional statement they gave us or it'll contradict a possible inference we could have made so when you read a must be false paragraph you should still use your normal inference brain to look for what sort of possible things you could infer by combining two or more ideas and remember that must be false doesn't mean which answer is making a bad unsupported inference illegal reversals and illegal negations are illegal inferences but they're not contradictions it's not about hey we didn't talk about that therefore it must be false anything out of scope could not possibly be contradicted you can only contradict something that you know about but must be false is saying something we do know is wrong let's take a look at a real example from test 71 pause the recording try this problem on your own for about a minute and a half and then unpause when you're ready to talk about it this is a very atypical phrasing for a must be false type of question it's talking about violating the principle the word principle almost always means a conditional claim on LSAT so must be false would have us thinking conditional and principle would also have us thinking conditional sure enough the word unless is there unless is a very common conditional trigger word and one of the easiest ways to always know you're setting it up correctly is to learn that unless is the same as if not the if part of a rule goes on the left and if not is just saying we'll put the negated version of this on the left the idea that comes after unless is that your purpose is acting in the interest of some other person since we are thinking okay if not we're going to say if your purpose is not acting in the interest of another person then you should not intentionally misrepresent their beliefs all right so we have a principle its conditional rule we used unless if not to make sure we set it up correctly now we have to think all right what does it mean to violate a principle it means to contradict a conditional and the form for that is I need a counter example where the trigger happens but the outcome doesn't so we can anticipate an answer that would sound like the left side happens somebody was not acting in the interest of somebody else but the outcome is opposite of what it should be this person does intentionally misrepresent to the other person's beliefs if you want you can pause the recording one more time to double-check your answer to see whether it gives you the blue and the red let's look at choice a if we're wondering whether or not an was acting in the interest of Bruce that last idea says she was definitely not acting in his interest in fact she just wanted to make him look ridiculous okay so we've established the trigger now we want to see an does intentionally misrepresent Bruce's beliefs she tells someone that Bruce thought that the moon landing was a hoax even though she knows he doesn't think this okay well so then yes she definitely intentionally misrepresented Bruce Bruce's beliefs it looks like this is our correct answer because it triggered the rule but then gave us the opposite of what the outcome told us we should do let's check the other answers to feel better about picking hey B says that Claude told someone Thelma believes in aliens even though he knew that wasn't the truth but he wanted to keep this other person from bothering her so first we wanted to know is Claude acting or not acting in the interest of Thelma he is acting in her interest that last idea is saying he was just trying to keep someone from bothering Thelma so we don't get off the ground on this one the other part is right I mean he does intentionally misrepresent her beliefs but because he does so for her sake it isn't covered by this principle this principle only covers cases when you aren't acting in the interest of the other person we can get rid of B when we scan see trying to figure out whether or not one person was acting in the interests of another we can see that the motivation was he wanted these people to think highly of Maria so it sounds like he's acting in Maria's interest that means that again we're not gonna get anywhere with this because we didn't establish that blew the trigger that says he wasn't acting in their interest and he intentionally misrepresented her beliefs we also don't really know whether he misrepresented Maria's beliefs all we know is that Maria didn't want him to say a certain thing but it may have been a true belief Maria had so it doesn't match the trigger but it also doesn't clearly match the outcome as well when it comes to D what are the motivations of Harvey he said what he said because he thought she would like him as a result all right so Harvey is saying something not in the interest of somebody else but in his own selfish interests he's not acting in the interest of Josephine does he intentionally misrepresent Josephine's beliefs no he intentionally misrepresents his beliefs eagle-eyes about thinking that shall one day be famous but that's not covered by the rule this rule is saying you shouldn't intentionally misrepresent what other people believe it doesn't say whether or not we're allowed to intentionally misrepresent our own beliefs get rid of D because it doesn't match the outcome when we look at e and we check on Wanda's motivations she is just trying to embarrass George she wants people to know that George is a geography fool okay so we've established the blue she's not acting in the interest of George does she intentionally misrepresent George's beliefs we know from this paragraph that Wanda knows that Egypt isn't really in Asia but we don't know whether or not George genuinely believes that she might be correctly representing Georgia's silly belief that Egypt is in Asia since we don't know whether or not George actually believes Egypt is in Asia we can't tell whether she's misrepresenting his belief or correctly representing it thus this answer does establish the blue trigger but it's not clearly delivering that red outcome so a is our correct answer we were trying to violate a principle we knew we'd be getting a conditional rule and we know that violating or contradicting a conditional means that you establish the trigger is happening but then say the outcome isn't so we picked an answer where somebody was not acting in the interest of someone else and was just trying to make Bruce look silly and she did intentionally misrepresent his beliefs she told people that he thinks the moon landing is a hoax even though she knows he doesn't actually think that conditional logic is the name of the game and must be false the vast majority of these end up testing conditional logic one way or another let's take a look at one more example pause the recording give this one a try for about a minute and a half and then unpause when you're ready to talk about it welcome back this question stem gives us the could be true accept wording when we go to this paragraph do we see any conditional logic this time yes we actually see quite a bit to only win until essential if yes those are all conditional logic trigger words it's about 15 or 20 words we should memorize that show up a lot to introduce conditional logic and we want to memorize for each word whether it introduces a sufficient condition that we would put on the left side of the arrow whether it introduces the necessary condition that we would put on the right side of the arrow or whether it's one of those special if not words like unless that we saw in the previous problem the most common sufficient triggers are things like if when where whenever wherever any Universal like all each and every and the only is a sneaky little counter example because only an only if and only when are the most common necessary trigger words you'll also see words that sound like a guarantee things that ensure imply guarantee always lead to something else introduce a right side idea and words that introduce necessity before it we're saying that we require something we need it we depend on it that thing also would go on the right side on the necessary side in fact it's just really nice to remember that if it's required it goes on the right and then we have these three words unless until and without where the rule that you want to memorize is that you will put whatever idea comes after that word on the left side of the arrow but a negated version so if not is saying you treat it like if in that you put it on the left side but you need to put the negated version so returning to this paragraph the first one we saw was only when which is just like only if it introduces a right side idea a necessary condition so helping students become independent learners has to be on the right side of the arrow and that means being an effective teacher goes on the left in our second sentence we see until which is an if not so we need to put on the left side if teachers do not have the power to make decisions in their own classrooms the tricky thing here is that the other idea needs the not that appeared earlier in the sentence we're saying if teachers don't have the power to make decisions in their own classroom then they can not enable their students to make their own decisions this was a weird phrasing where I could say until you clean up your room you cannot have dessert but I also could have said not until you clean up your room can you have dessert they would mean the same thing the third sentence gives us the word essential which is a synonym for necessity so I would ask myself all right what's the required thing in this sentence if you're telling me that students capability to make their own decisions is essential it's required then I know that idea goes on the right side of the arrow so I need students are capable of making their own decisions on the right side becoming an independent learner then takes the left side we can read conditional statements as the left side requires the right side so I can read this conditional as becoming an independent learner requires that they're able to make their own decisions lastly the final sentence uses if the classic that put it on the left side so if teachers are effective then they must have the power to make classroom decisions one bizarre thing about this question stem is that it said we were going to be reading an argument and still being asked what must be false so I wasn't sure if we would have to treat assumptions as though they are true but before I even get there I just want to figure out what's going on with all this conditional logic when we get more than one conditional logic rule they often linked together so we want to look to see do they have any repeating ideas well effective teachers showed up twice becoming an independent learner showed up twice having the power to make classroom decisions showed up twice and being able for students to make their own decisions showed up twice all right let's pull out that first rule if you're an effective teacher you can help your student become an independent learner can we chain to that sure we have a rule that says if the students are becoming independent learners then they must be able to make their own decisions can we change anything onto that well I see a rule about students making their own decisions but I would need to contra pose it to chained it on so I will I'll think alright if students are able to make their own decisions then the teachers did have power to make classroom decisions those first three ideas chained a to B B to C C to D so let's synthesize it and make this look a little bit easier if you're an effective teacher can help your student become an independent learner which means that student is able to make his/her own decisions which means that you the teacher clearly had the power to make classroom decisions when we look at our conclusion we realize there's really not a new thought happening there that was just a correctly derived conclusion effective teacher implies power to make classroom decisions so I don't have to worry about whether or not there were assumptions that we should also be treating is true because this argument was actually a valid argument the conclusion just summarizes our conditional chain if we're gonna find something that must be false and we have a big old conditional chain and we should again be reminding herself that's going to sound like you are the trigger but you're not the outcome but the question stem was actually even more specific it said what would we know about teachers who have enabled students to make their own decisions so that's our third link and when that is true it tells us that fourth idea we know that if the students are able to make their own decisions these teachers apparently have the power to make classroom decisions so we can infer these teachers definitely have power to make their own classroom decisions but we can't go backwards in a conditional chain so I have no idea whether they're effective I have no idea whether they are helping their students become independent learners when we look at the answers we can see that D is actually giving us that inference that must be true they definitely have the power to make decisions so D is wrong we're looking for something that must be false and D must be true a B and C are dealing with those unknowns we don't have the ability to go backwards so we have no idea whether or not they're effective we have no idea whether or not they're helping their students become independent learners II mean while contradicts the inference we were able to make we know they have the power to make decisions in their classroom so II is contradicting that saying no they don't they don't have the power so he is our correct answer D was something that must be true that actually was the available inference a B and C were just toss ups they could go either way we have no idea all right so once again how do we spot must be false questions it might say must be false might say cannot be true could be true except least compatible or violates the principle the most common reasoning structure by far will be conditional logic most correct answers will either contradict a conditional rule or they'll contradict some available inference that we could have made by combining ideas when it comes to trap answers you could lump them all together and just say well they all could be true but when we think about how the test writers design them we could get a little bit more granular some things are unopposed meaning they certainly fit within the information we were given if I say that somebody uses a wet-nap after they eat shrimp it's certainly unopposed to say they also use it before they eat the shrimp out of scope is really referring to bringing up brand-new things we never talked about bringing up a brand new thing means that there's no possible way we could contradict it because we didn't even get any information about it in the first place supported is more like an answer that is a valid inference or sounds like it pretty reasonably goes along with the paragraph we're looking for something that starkly goes against the paragraph reversal negation refer to ideas that are tempting because we know it's an incorrect manipulation of a conditional logic rule it's not a valid inference but it's not that's not the same thing as contradicting a rule finally some answers will be too weak to contradict which is sort of like saying unopposed that they could still fit within the margins of the fax we were told if I'm told that most clowns are scary and an answer says some clowns are really nice and welcoming that doesn't contradict it's too weak there's room for some clowns to be nice when I've only said most clowns are scary all right thanks a lot for learning with us please check out any of our other videos on YouTube or join us on lsat lab comm