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Flaws are a HUGE part of the LSAT. correctly identifying a flaw or even having a remote sense of what it is, helps with looking for the right answer choice and this helps with both accuracy and speed. I've complied a list that addressees a lot of the common flaws. While it's not exhaustive, its pretty thorough. I've used various posts on here, various guides on here, 7sage blog posts, LSAT trainer, MSLAT LR book, LG Bible, and LSAT blog posts to compile it. This isn't revolutionary, but is a good source with a nice complied list of terms you can add to your LSAT dictionary when attacking the LR section.

Please don't try to memorize this list and try to catergorzie every assumption tree question into these categories. it won't work. but rather memorize it or be familar with it so that you are actively thinking about these when attacking the gaps/flaws. just by doing this, i think you can greatly improve your score.

if any of the "seasoned" TLS posters want to add something or want to let me know how to improve this, please post on here or PM me. i really want to make this useful for me and future takers of the LSAT using TLS as a resource.

the mods can contact me if this is some sort of rule breaking post.

hope the following guide helps:

Attacking the source of the argument
-any argument that attacks the motives, past actions or arguments of author, the author himself, or the source of information are flaws

Uses terms unclearly/equivocation
-author uses a term inconsistently (meaning using a term with more than meaning)
-look for terms/words that are repeated in the premises and conclusion. See if they author has slightly changed or altered the meaning of them

Failed analogies
- most analogies fail because they loose their relevant similarities
-generally they are too dissimilar to the original situation to be applicable

Appeal Fallacies
-appealing to authority in an area outside their expertise
-this happens when an author appeals to an authority where the subject matter is outside the expertise of the authority (i.e. a lawyer’s opinion on the specification of a certain wing of a spacecraft)
-appeal to authority
-when the author cites an opinion of an authority of the given subject matter and uses that to draw his conclusion
-appeal to numbers
-states a position is true because the majority believes it to be true
-appeal to emotion
-uses emotional language cues to draw out the conclusion

Causation errors
-if you see any sort of causation words (i.e. led to, is caused by) or notice there is a causation between A and B (or even A+ A1 + A2 caused B), the flaw is that: there may be another explanation for the stated relationship
-the 4 most common types of alternate relationships that are addressed by answer choices are:
-reverse is true (B caused A)
-something outside caused it (C caused both A and B)
-relationship is coincidentally correlated and really something else caused B
-A and B have an impact on each other/ not a causation relationship

Percentages v. quantity
-anytime you see a percentage and quantity being related to draw out a conclusion, be aware of this flaw: percentages don’t necessarily reveal quantity and quantity don’t necessarily reveal quality

Confusing probability for certainty
-be aware of arguments that say since a certain premise could be true, it must be true

False dichotomy
-author assumes there are only two options/course of action when there may be others

Survey to reach a general conclusion
-whenever you come across a survey in the stimulus being used to support a conclusion, be aware of the following things:
-does it use a biased sample?
-are the questions structured properly?
-do the respondents give accurate/appropriate responses?
-remember only a random/non-biased survey can be used to represent general conclusions (aka: if a survey targets a certain group and uses evidence from that to project it on the entire nation, which includes other groups not tested, it is a flaw)

Generalization
-author makes a generalization based on a small sample size or based on one or two incidents
-in other words: author takes a small number of instances and treats those instances as if they support a broad, sweeping conclusion

Experiments
-anytime you read a stimulus with an experiment, be on the lookout for control groups
-experiments to reach a general conclusion must include a control group/ it must also establish the baseline of what is measured before the experiment begins

Use of evidence
-this is something you should check for in most arguments because most/if not all use evidence
-check for the following major flaws with using evidence to reach a conclusion:
-“your argument fails therefore the opposite of your conclusion must be true”
- presuming that because a claim has been poorly argued, or a fallacy has been made, that it is necessarily wrong
-lack of evidence for a position is taken to prove that position is false
-lack of evidence against a position is taken to prove that position is true
-some evidence against a position is taken to prove that position is false
-some evidence for a position is taken to prove that position is true

Part and whole relationship errors:
-assumes what is true of part of a group is true for the whole group and/or to each member of that group
-assumes what is true of the whole group and attributes it to part/or to each member of the group

Red herring:
-argument doesn’t address the relevant issue but rather issues a tangential issue or has nothing to do with the relevant issue

Confusing one possible solution for the only solution
-just because one solution solves a problem doesn’t mean that particular solution is the only solution that can solve the problem.
-opposite is a flaw as well: just because one solution to a problem is inadequate doesn’t mean that the problem itself cannot be solved.

New v. Old
-just because something is old/traditional doesn’t mean it is right or better
-just because something is new doesn’t mean it’s the best course of action or that the old idea is not longer relevant or true

Past v. Future
-involves assuming that conditions will remain constant over time, and that what was the case in the past will be the case in the present or future

Relative v. absolute comparisons and conclusions
-being relatively better/worse at something does not mean that thing is absolutely better/worse at that something (i.e. A is smarter than B, therefore A is smart. This is flawed)

Descriptive v. Prescriptive
-descriptive: describes the current state and prescriptive: reveals what we should do
-on lsat, generally the trend is: descriptive premise → prescriptive conclusion
- the correct answer needs to bridge the premise to the conclusion

Conditional logic errors
-anytime you sense a conditional diagram is needed or the stimulus uses a lot of conditional language, look for these conditional logic errors that are regular on the lsat:
-confusing necessary and sufficient conditions
-mistaken negation
-mistaken reversal

Circular reasoning
-assuming what you’re trying to prove
-how to spot it: the premise is a restatement of the conclusion

Internal contradiction:
-makes conflicting statements in the premise and conclusion relationship

Straw Man
- misrepresenting someone's argument to make it easier to attack

Falsely equates characteristics:
-falsely equates ‘not’ being something with being the same sort of ‘opposite’ of that thing

i'll add more and edit and condense this post as i progress towards my September lsat. Hope this helps y'all.

Just posting to say thanks for taking the time to do that and post it.

Bookmarked. Thanks for the hard work; looks great!

Nice work. The longer I teach the LSAT, the more I'm convinced that these flaws are actually VERY important to LR. People hit a wall studying question types. Those are easy to master, books teach them. I've found no reliable way to learn flaws other than experience.

I suspect memorization might work, but I'm not sure. In my experience, people read about these, nod, and then totally miss them in practice. I think the most useful way to use this list is to print a copy and use it on review. Categorize the flaws in LR questions. See the flaws.

I notice these flaws time and again. I have written explanations for a few thousand LR questions now. It's at the point where I scan a question and see "UGH, another is/ought switch. C'MON people, why can't you see these?" (That's descriptive vs. prescriptive from the list, they're everywhere)

But then I remind myself that I didn't see these when I started out. I just did a bunch of questions, and started to notice trends. Noticing - that's the key. Take this list, and look for them. They're all over the place. And once you see them a few times, you learn the patterns, and you see LR the way experts see it.

------------
Couple questions OP:

1. Do you have any examples of questions that use straw man? I can't recall any.
2. Likewise, false equation: do you have an example? It doesn't ring a bell, but I may not have understood your description. You mean like "opposite of hot is not cold"?
3. Likewise, internal contradiction is not one I recognize.
4. Red herring: any examples?
5. I would add one to experiments: assuming test subjects must be heterogeneous. I've seen this in a bunch of answers. A study is stronger if the test subjects are NOT all the same. You normally want the sample to be randomly selected from the population. People seem to be assuming that identical subjects = controlled experiment, which is not how science works.
6. typo in causation --> I think you meant no impact
7. An appeal to relevant authority is actually NOT a flaw on the LSAT. Many questions quote an expert and use it as evidence. An appeal to authority is only wrong in the case of an irrelevant expert. E.g. Linda the scientist saying no scientists like poets. Linda is not an expert on scientists. That question (it's a parallel flaw) has multiple examples of relevant authority in good arguments in the answer choices.

I like your guide overall. Anything I *didn't* comment on, I think is correct. You've caught the main ones. Especially:

* relative vs. absolute
* causation
* number vs. percentage
* descriptive vs. prescriptive

I see those over and over. Everyone should know them.

Love this thread! One thing I might consider is whether these flaws consolidate further. For example...

One might look at the following flaws and see them simply as misguided comparisons:

Parts to Whole
Past vs Future
Relative vs Absolute
Probability vs Certainty
Percentages vs Amount
Failed Analogies
Equivocation

Graeme, glad to see you at work here, and for sure some of the ones you brought up aren't common on the LSAT. Here are two though for future use:

Graeme (Hacking the LSAT) wrote:1. Do you have any examples of questions that use straw man? I can't recall any.

PT7, S4, Q9

Graeme (Hacking the LSAT) wrote:3. Likewise, internal contradiction is not one I recognize.

PT20, S1, Q22

matt@manhattanlsat wrote:
Graeme, glad to see you at work here, and for sure some of the ones you brought up aren't common on the LSAT. Here are two though for future use:

Graeme (Hacking the LSAT) wrote:1. Do you have any examples of questions that use straw man? I can't recall any.

PT7, S4, Q9

Graeme (Hacking the LSAT) wrote:3. Likewise, internal contradiction is not one I recognize.

PT20, S1, Q22

Thanks, good catch. Do they ever appear on modern tests? (39 onwards)

I'd love to quantify the flaws used. What are the most common ones? What percent of flaws are they? But that's a big, big project.

I think misguided comparisons is a good way of categorizing what they fall under. The question "are these the same thing" should always be on your mind. I think the subcategories are very useful for helping notice that the comparisons are wrong.

Just wanted to say thanks for the time and effort put into this guide. I plan on printing it out to use with my studies

Great writeup. It's awesome for you that you took the time to note all of these. I just wanted to point out one thing that you could condense to help bring the disparate pieces together.

cavalier2015 wrote:Conditional logic errors
anytime you sense a conditional diagram is needed or the stimulus uses a lot of conditional language, look for these conditional logic errors that are regular on the lsat:
-confusing necessary and sufficient conditions
-mistaken negation
-mistaken reversal

The second and third points (MN and MR) are actually the exact same as the first point (confusing necessary and sufficient conditions). Or rather, they are simply ways of categorizing the flaw in the first point. Once you make that connection, it's best to just forget the phrases "Mistaken Negation," and "Mistaken Reversal," because what's really going on is a confusion between what is necessary and what is sufficient for a condition. I'm going to use some definitions to show why:

Mistaken Negation --- when the author of an argument infers, based upon the absence of one condition which would guarantee a certain outcome, that the outcome itself must be absent. The flaw here is that the author assumes that the sufficient condition is the only one which would guarantee the outcome. If that were not the case, meaning if there are other conditions which would guarantee the outcome and those haven't been eliminated, then it's not necessarily true that the absence of one particular sufficient condition results in the absence of that condition's requirement. This is represented by the following argument structure:

Rule: A ---> B
Fact: A
_____________________
Concl: B

The assumption is that the outcome B requires A. Which we can represent as "B ---> A."

Mistaken Reversal --- an invalid inference which infers that a sufficient condition is present because a requirement of that condition is also present. Meaning, it infers that the necessary condition is sufficient when that hasn't been established. Another way of saying this is that the author assumes that the sufficient condition is the only one for, and is thus required by, the outcome. The flaw here is the same as the Mistaken Negation. The only way we could make this inference is if we know that the sufficient condition is the only thing that is sufficient for its requirement. This is represented by the following argument structure:

Rule: A ---> B
Fact: B
_____________________
Concl: A

The assumption is that the outcome B requires A. Which we can represent as "B ---> A."

Note that the assumption is the exact same, I actually copied and pasted the preceding sentence because there was no point in typing the exact same thing twice. This is the reason why you should look beyond the labels "Mistaken Negation," and "Mistaken Reversal." Both phrases explain the underlying situation, which is a confusion between what is sufficient for a given outcome and what is required for that outcome to occur. Once you recognize that, there's no point in phrasing the flaw in these two ways because the confusion is the flaw, these two phrases simply help you understand why that flaw is present. If that reason isn't enough, then it's important to point out that the flaw will likely be stated in the answers not in terms of these phrases but in one of the following ways, which establish a confusion between sufficient and necessary conditions:

1. Assumes that a condition which is enough for [would guarantee/requires/sufficient/always results in/ensures/assures/necessitates/etc.] a given outcome is required for that outcome to occur.

1. Overlooks the possibility that there are other ways for the outcome to occur [that the requirement could occur without the sufficient condition/etc.]

You may very well understand all of this, and if so then I've kind of droned on haha, but the way in which you listed it implies that the three points are different in some way so I thought I'd point out that far from being different, they are actually the same. Anyways, good luck with the September test.

I have an idea!

Lets find a question that addresses each flaw. …that way there is an example in case someone doesn't understand or needs to see it.

Obviously we can't post the official questions on here however we can post where we can find it. Ex-PT59 Sec 3 Q5.

Good Idea^
False Dichotomy
PT66, Section 1, Number 1

CardozoLaw09 wrote:Good Idea^
False Dichotomy
PT66, Section 1, Number 1

Love it! We already have one...I'll try and find more!

Graeme (Hacking the LSAT) wrote: Nice work. The longer I teach the LSAT, the more I'm convinced that these flaws are actually VERY important to LR. People hit a wall studying question types. Those are easy to master, books teach them. I've found no reliable way to learn flaws other than experience.

I suspect memorization might work, but I'm not sure. In my experience, people read about these, nod, and then totally miss them in practice. I think the most useful way to use this list is to print a copy and use it on review. Categorize the flaws in LR questions. See the flaws.

A few weeks ago I read an old post from one of the Manhattan LSAT guys suggesting the same thing so I started doing that. I went through some recently completed PTs and started categorizing the questions by Flaw Type. I have good memory (like most people on TLS) so I can memorize those flaw verbatim BUT actually RECOGNIZING them in arguments when the clock is tricking is really HARD. This method is helping me alot. THANKS MLSAT guy and Greame. Below is a screen shot of my spreadsheet if your interested in my method (excuse my spelling/grammar, I don't really spell check excel documents, plus the "e" on my laptop is acting up ):

(LinkRemoved)

I have not really drilled Assumption Family Questions (using Cambridge) but I plan to do so within this week. When I am done, I will add to the list. However, their is a list (partial) of common LSAT flaws with PT#S#Q# on the LSATblog, here is the link:

http://lsatblog.blogspot.com/2012/09/ls ... acies.html

Side note: This is my first picture post on TLS (yay me ), it took me forever to figure out how to post a pic though

Edit: changed "really good memory" to "good memory", old age is getting the better of me

just wanted to add a bit more that I found helpful (some are repeats from my original post but with some amended information):

Ascriptive argument
-the error: describe position to some third party then refute it and then assume our
evidence matters
-assuming the refuting evidence matters

Prescriptive argument
-anytime we are given something we should do, ought to do, must do, we need to do
-every time you see this, the author is assuming the prescriptive actually works

False choice
-anytime an arguments lists of factors and then says since we cannot do some of the factors, we should do the other factors
-arriving at the last choice is a flaw
-eliminate certain choices and then says we have to do any other option → false choice

Sampling Flaws
-assumption that the sample is in fact representative for the wider population
-questions of representativeness, did the sample look different before

Ad Hominem
-“to the man” fallacy/ confusion of person to argument
-flaw: constructing argument around the person rather than the evidence or reasoning
-personal characteristics has no bearing on prescriptive conclusions (supporting or not supporting)
-not even if they are hypocrites

Absence of evidence
-absence of evidence is not causation

Equivocation
-wrong answer choice a lot, “the author equivocates..”
-same word in two different ways → flaw

Failed analogies
- most analogies fail because they loose their relevant similarities
-generally they are too dissimilar to the original situation to be applicable
-if it compares two cases, make sure the two cases are comparable
-anytime we see a case made between two separate things, we should ask “are these two things comparable”


Causation errors
-if you see any sort of causation the flaw is that: there may be another explanation for the stated relationship OR in other words → the speaker believes the state case is the only cause for the effect
-the 4 most common types of alternate relationships
-reverse is true (B caused A)
-something outside caused it (C caused both A and B)
-relationship is coincidentally correlated and really something else caused B
-A and B do not have an impact on each other/ not a causation relationship
-no other alternative explanations
For weaken questions: how the LSAT undermines causation→
-Alternative cause
-cause without effect
-effect without cause
-relationship reversed
-statistical problem exists with the data used to make the causal statement
For strengthen and assumption questions:
-eliminate alternate cause
-when cause occurs, effect occurs
-when cause does not occur, effect does not occur
-eliminate relationship reversed
-data used to make causal statement is accurate/ eliminate problems with data
Correlation/causation issues are best solved by doing a few things:
- Show that same cause produced the same effect in an analogous situation
- Show that the absence of the cause produced the absence of the effect
- Show that the effect didn't actually cause the cause
- Rule out an alternate explanation

Percentages v. quantity
-anytime you see a percentage and quantity being related to draw out a conclusion, be aware of this flaw: percentages don’t necessarily reveal quantity and quantity don’t necessarily reveal quality
- you need to take a close look at which groups are being discussed
- we must know the content of each proportion being looked at
Misconceptions:
-Increasing % = increasing numbers
-Decreasing %= decreasing numbers
-Increasing numbers = increasing %
-Decreasing numbers = decreasing %
-Large numbers = large percentages OR small numbers = small percentages
-Large % = large numbers OR small % = small numbers
For MBT with this logic:
-if stimulus contains % or proportion information only, avoid answer choices that contain hard numbers
-if stimulus contains only numerical information, avoid answer choices that contain % or proportion
-if stimulus contains both % and numerical information, any answer choice that contains numbers, %, or both may be true
For Weaken and Strengthen questions
-look carefully for information about the total amount

Conditional logic errors
-mistaken Reversal, mistaken Negation
-mixing up necessary and sufficient questions
For Necessary Assumption questions:
-if preemies contain conditionals and conclusion is conditional, correct answer will supply the missing link in the chain
-if only conclusion has conditional, the correct answer will deny scenarios where the sufficient condition occurs and the necessary does not. Meaning, correct answer always protects the necessary condition

love this guide, thanks for this list!

Good work on this. But be careful with spending too much time trying to memorize 100 argument types. Most of the things you listed are either variations on the same theme or show up once every 2-3 years at best.

Flaw questions are like the rest of the assumption family: the vast majority of them fall into one of two fundamental camps. And the LSAT makes some of them more likely than others.

The most common for flaw stims is Overlooked Possibilities (Author's conclusion is too strong for the evidence) [Also most likely arg for Str/Wk and about 50% of Nec Assumption Qs; Rare in Suff Assump Qs]

-May be very generic (Going to school because I can't go to work)
~May come in the form of causation (author assumes there's no other cause, that the two aren't merely correlated, and that the causation isn't reversed)
~Author confuses Necessity for Sufficiency or vice versa (as pointed out by someone else, it just means jacked up formal logic. Either they negated without flipping or flipped without negating)

Virtually every LSAT is going to have a hand full of the first, one or two of the second, and one or two of the third in their flaw Q set.

Scope Shifts: Author relies on irrelevant evidence to support a conclusion [Also: Maybe 20% of Str/Wk- mostly Str-, virtually all of Suff Assump., about 50% of Nec Assump)

-Alike (Author assumes two dissimilar things are alike in some way- people often refer to these as analogies "I am successful because I work hard")
-Different (Author assumes two things are mutually exclusive in some way. I'm not going to be successful because I work hard)
-Need Evidence For Conclusion (Author assumes you need the evidence for the conclusion. I'm not going to be successful because I don't work hard)
-Representative (Author uses one group in the evidence to draw a conclusion about another group)

Most LSATs will have one or two of the first, one or two of the last, and then one or two of the middle two combined.

90% of your Flaw Stims will fall into the categories above. Then about 10%- mostly the harder ones- are going to be your more uncommon argument types.

The next set of arguments to bother with are:

Possibility vs Certainty (shows up on occasion- once or twice a year in flaw questions)
Equivocation (shows up *maybe* once a year)
Bad Predictions (Author's conclusion is about the future based on evidence in the past) Shows up *maybe* once a year

Then you get to the rest of your list (unless I'm blanking on another type right now), which are extremely rare and not worth prepping unless/until you're at the point where you get almost all of your flaw questions right every time. If you do the math above, you'll realize that after they've gone through their staple argument types, there's just not a lot of room for the crazy ones. They only put so many flaw questions on any given test.

Hope that helps with study priorities.

wow thanks! quick question though: what do you mean by "may be very generic"?

cavalier2015 wrote:wow thanks! quick question though: what do you mean by "may be very generic"?

Basically, when I say generic OP I mean it's the standard "evidence and conclusion are related, but the conclusion goes too far" definition without any of the little twists like causation, pro/con (which I forgot to mention in the previous post- ooops), nec vs suff, poss vs certainty, etc (all of which are OP args)

If you want, here's some stuff I wrote up a while back. It's not pretty, but it might help.

Overlooked Possibilities Visual: https://cloud.box.com/s/7g4l3ahwk49t8tpbtbwl
Overlooked Possibilities Explanation: https://cloud.box.com/s/0pp1dfoibf9oi1ftnpus

Flaw Argument Types Visual: https://cloud.box.com/s/u9tp3px399o5l595gb1a