Fallacies and Argument Appraisal by Tindale | Excerpt

The following excerpt about the post hoc fallacy (a specific type of correlation-causation fallacy) is from Professor Christopher W. Tindale's Fallacies and Argument Appraisal.

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Online LSAT Logical Reasoning Video Course

My LSAT Logical Reasoning video course is now part of my full LSAT courses. 

They include exclusive access to attend my Live Online LSAT Master Classes + Q&As, and on-demand video lessons you can watch anytime. Plus, LSAT study plans to keep you on track. You can save hundreds of dollars with an LSAT package.

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For information about just the Logical Reasoning video course, start here:

I've been hard at work putting together the curriculum for a new LSAT course.

And I've just released the second part - a comprehensive online LSAT Logical Reasoning video course.

Why? Because the LSAT courses currently available cost far too much money, and they waste your time with overcomplicated methods and categorization systems.

Instead of making this a traditional classroom course, I've put it online:

-You'll be able to go at your own pace. Freed from having to go to LSAT class when you're tired after work or school, you'll be able to watch (and re-watch) all the course videos at any hour, day or night.

-You'll save a ton of money. By putting the course online, I can eliminate overhead expenses like rent. To keep costs low, I'm not wasting any money on advertising, and I've recorded all the videos myself, without hiring graphic designers to create special effects. I'm passing the savings on to you.


I'm not sure whether online videos are for me.

Watch some of my 180+ free LSAT explanation videos to get a sense of my style. Just keep in mind that the course videos are even more detailed.


I like your free videos, but what does the course include? 

I'm glad you asked. Through dozens of high-definition videos, I provide you with the fundamentals you need in order to effectively attack the Logical Reasoning section. I also give you a detailed overview of each Logical Reasoning type, as well as thorough walkthroughs of questions within each type.

Upon completing this course, you will be ready to take on the LSAT Logical Reasoning section.

Join now to improve your LSAT Logical Reasoning score today.




Still not convinced? Keep in mind that I'm offering all LSAT courses with a 100% money-back guarantee.

Try the LSAT course of your choice without risking a thing. If you don't love it, just email me within 30 days, and show me you're doing the exercises and not getting results. I'll give you a full and complete refund, and you can even keep all the books — at my expense.

I've made these literally risk-free to try.

Why would I offer a guarantee when I don't have to? I can offer this because I've rigorously tested my materials with thousands of students. I know they work, and I want this to be a no-brainer for you.

(By the way, I ask you to show me you've done the exercises because I know how effective they can be. I don't plan to keep your money if you're dissatisfied, but the only way to get results is to take action. I know you’re busy, but if you can’t commit to at least trying the exercises, then you shouldn’t join.)



Here's just some of the feedback I've gotten about my online LSAT courses:

"I did end up just going ahead and buying your online Logic Games course. I figured that it would be good value and clear instruction - everything I've seen on your blog has been. I went through the first 12 videos last night and it is very good. In the end it came down to yours and [another course], and your explanations just make more sense to me. Thanks!" - Joanne M.

"Just wanted to say thank you. I've made breakthrough after breakthrough thanks to your Logic Games course, and all the material you have available. It was all worth its weight in gold, and I truly admire you and appreciate what you are doing! I could not afford a Kaplan course, but even if I could have, I would have been crazy to choose it over your study plans/guides/posts etc.  I will be recommending you to anyone and everyone I know that is taking the LSAT. Thank you again!!!" - Miranda C.

"The Logic Games course is going great! Logic Games so far was my biggest weakness but I recently took a PrepTest and received only -6 on Logic Games after going through only a very tiny bit of your course. I want to hit a 165 and I feel your course is the last bit necessary…The course is a great review and also an extreme bargain." - C. T.


"I love the day-by-day study plan, your blog, and your online course. I've dabbled with Kaplan before and this works so much better for me." - Cheryl H.


"I've been working through your Logic Games course, and I really really like it. It's helped me improve so much on my games." - Sammy Z.

"I've taken your entire Logic Games course. First of all, thanks for a great learning experience. I feel much better prepared than I did before I started." - Nathan Y.


"I'm in the Logic Games course and I love it!" - John D.

"I'm a fan of your blog. Your online Logic Games course helped bring a clarity no other resources could provide...Thanks for your help Steve! Keep all the great work you do." - Jon H.

"The course has been extremely beneficial thus far!" - Kadeem R.


"I just wanted to thank-you for your great LSAT logical reasoning course. I got a 166 in October, up from a 159 in June and the difference was the logical reasoning sections, as  I went from 16 wrong to 6 wrong in the 2 sections combined." - Alex W.

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Questions? Shoot me an email at lsatunplugged@gmail.com

Remember, the course is 100% risk-free. That means you can try it, then decide if it's right for you. If you don't love it, just show me you did the work, and I'll refund 100% of your money. But I'm confident this will help you improve your LSAT score and get into the law school of your dreams.

Get started now.

Online LSAT Logical Reasoning Video Course Syllabus

Because I want you to see exactly what you'll be getting in my online LSAT Logical Reasoning video course, I'm including the entire syllabus below.

These are the contents of the course.




General Thoughts on Logical Reasoning

Introduction to Logical Reasoning

Overview: Types of Logical Reasoning Questions

Habits of Top Scorers

Logical Reasoning Approach


Conditionality (Sufficient and Necessary Conditions)

Introduction to Sufficient and Necessary Conditions

The Contrapositive (Simple)

Failed Contrapositive Attempts: Inverse and Converse

The Contrapositive (Complex)

Connecting Conditional Statements

Reading Conditional Chains

Translating Except, Unless, Until, and Without

Sufficient / Necessary Conditions and Time

Difference Between Formal and Informal Logic


Term Identification

Distinguishing Between Evidence and Conclusion

Numbers / Quantifiers: All, Most, Several, Many, Some, None

Inference Logical Reasoning Questions

Must Be True Questions

Most Strongly Supported Questions

Main Conclusion Questions

Main Point Questions

Complete the Argument Questions

"Assumption" Questions

Necessary Assumption Questions

Negating Conditional Statements

Sufficient Assumption Questions

Difference Between Necessary & Sufficient Assumption Questions

Help / Hurt Questions

Strengthen Questions

Weaken Questions

Flaw Questions

Common Logical Reasoning Flaws

Flaw Questions


Parallel / Principle Questions

Parallel Reasoning Questions

Parallel Flaw Questions

Principle-Application Questions

Principle Questions


Abstract / "Meta" / Identify Questions

Point At Issue Questions

Resolve the Paradox Questions

Method of Reasoning Questions

Role of a Statement Questions



Analyzing the Stimulus on a Deeper Level

Thinking About the Stimulus



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Questions? Shoot me an email at lsatunplugged@gmail.com

LSAT Logic and the 2012 Mayan Apocalypse

Many believe the Mayans predicted that the end of the world would occur in December 2012.

In this post, LSAT Blog reader Sami analyzes that claim. Please feel free to discuss her analysis, and the imminent doom we may be facing, in the comments.

If you'd like to write a post for LSAT Blog with your own analysis of the Mayan prophecy, or any other real-life situation, please email me. I'd love to feature you!

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LSAT Logical Reasoning Flaws, Fallacies List

The LSAT Logical Reasoning section tests your ability to spot a variety of flaws. Some are as simple as failing to consider a particular possibility, but we can group the others into the category of classic logical fallacies. They're the type you find in basic logic textbooks.

Many Logical Reasoning questions describe flaws in the abstract, but most speak in terms of the stimulus topic. They'll say things like: "the arguments fails to consider...(something specific to the topic of that argument)." However, even when the stimulus talks in terms related to that argument, it often refers to a classic flaw.

*** Download my free Common LSAT Flaws PDF here ***

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Media Argumentation by Douglas Walton | Excerpt

The following excerpt about evaluating appeals to expert opinion (aka appeal to authority) is from Professor Douglas Walton's Media Argumentation: Dialectic, Persuasion, and Rhetoric.

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Fundamentals of Critical Argumentation by Douglas Walton | Excerpt

The following excerpt about the correlation-causation fallacy is from Professor Douglas Walton's Fundamentals of Critical Argumentation.

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Informal Logic by Douglas Walton | Excerpt

The following excerpt about the correlation-causation fallacy is from Professor Douglas Walton's Informal Logic: A Pragmatic Approach.

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LSAT Logic and Prescription Drug Addiction

LSAT Blog reader Jamie wrote the following LSAT-style analysis of a recent NYTimes article on prescription drug abuse. Please feel free to discuss her analysis, and the article itself, in the comments.

If you'd like to write a post for LSAT Blog with your own analysis of any real-world situation, please email me. I'd love to feature you!

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LSAT Logic: Interpreting Survey Data | Polls

LSAT Blog reader Rachel wrote the following LSAT-style analysis of survey data on abortion and gay marriage. Please feel free to discuss her analysis, and the surveys themselves, in the comments.

If you'd like to write a post for LSAT Blog with your own analysis of any real-world situation, please email me. I'd love to feature you!

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LSAT Studying Makes You Smarter | Proof?

We recently learned that playing a memory game may improve your LSAT score.

Researchers have also found that LSAT studying may also make you "smarter."

The evidence comes from a recent study in which a group of students who studied for the LSAT for 3 months improved their reasoning abilities far more than those in a control group:

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Why are Pre-Law Students Losing Interest in Political Careers?

The percentage of pre-law students considering a career in politics has dropped from 54% in 2009 to 38% today, according to recent survey results.

This decline was preceded by a similar drop in the percentage of lawyers in Congress over the past 4 decades.

I turned to my pre-law audience for answers, and the explanations I received generally fell into two broad categories:

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Is It Wrong To Analyze The Trayvon Martin Shooting?

Is it wrong to analyze the logic of arguments related to the Trayvon Martin shooting?

One commenter thinks so. My response:

In December 2010, I wrote about the logical fallacies surrounding the military's "don't ask, don't tell" policy. A commenter responded, "There is a point where LSAT logic holds no relevance in this argument..."

Being an LSAT tutor, I believe logic is always relevant, whether it's finding a flaw in an argument, a weakness in it, or a principle underlying it. And, fine, I'll admit that I live and breathe this logic stuff.

So a little part of me died inside when I got a somewhat-similar comment on this week's blog post analyzing the logic surrounding the Trayvon Martin case:

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LSAT Logic and the Trayvon Martin Shooting

LSAT Blog reader Julie wrote the following LSAT-style analysis of the Trayvon Martin shooting. Please feel free to discuss her analysis, and the Trayvon Martin case itself, in the comments.

If you'd like to write a post for LSAT Blog with your own analysis of the Trayvon Martin shooting or any other real-life situation, please email me. I'd love to feature you!

Read more »

Logic of Real Arguments by Alec Fisher | Excerpt

The following excerpt about analyzing arguments is from Professor Alec Fisher's The Logic of Real Arguments.

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Logical Reasoning: Necessary and Sufficient Conditions

LSAT Blog reader Vicky recently wrote with the following:

"I know you have already covered the sufficient and necessary conditions quite extensively, but there are still many (myself included) who are still stymied by it.

If you feel that the explanation I provide below is accurate and acceptable, posting it as an introductory Logical Reasoning topic might help other LSAT students."

I found Vicky's explanation to be useful and have included an edited version of it below.

Read more »

Negation and Necessary Assumption Questions

In this blog post, I discuss a common, and effective, strategy for approaching necessary assumption questions.

I also talk about shortcomings in the way prep companies often teach test-takers to think about necessary assumption questions.

Finally, I give some examples of necessary assumption questions and explain some frequent patterns in each.


A Common and Effective Strategy for Necessary Assumption Questions: The "Negation" / "Denial" test

As the name implies, this "test" requires you to negate each of the answer choices. The correct answer choice, when negated, renders the argument invalid. The argument cannot be valid if the necessary assumption is not true. After all, the necessary assumption is, in fact, necessary for the argument to work

I agree with the consensus that this is a good way to approach necessary assumption questions.


How does this work in practice?

Ask yourself as you read each answer choice, does this *need* to be true for the evidence to require the conclusion?

Well, if it weren't true, what would happen? Would the argument be able to coexist with the negated answer choice?

If it would not be able to, then it is the necessary assumption, so it's our answer.

Again, the correct answer choice needs to be true in order for the argument to work. As the common question stems suggest (examples of those in Difference Between Necessary and Sufficient Assumption Questions), the argument depends upon the assumption being true, requires that it is true, and assumes that it is true.


A Quick Note on Negating Answer Choices

Make sure to translate the answer choice into its logical opposite, not its polar opposite.

Example:

The polar opposite of the statement "All people are standing" is "All people are not standing." In English, that means "No people are standing." It's the other extreme. We don't want this.

The logical opposite of the statement "All people are standing" would be, "It is not the case that all people are standing." In English, that means "Not all people are standing" or "Some people are not standing."



Necessary Assumption Questions Do Not Bring in New Information


Many categorization systems correctly place Must Be True questions under the umbrella of Inference questions (those asking for information we already know to be true based on the stimulus).

However, they typically categorize Necessary Assumption questions differently, placing them with  Strengthen and Sufficient Assumption questions. This is a mistake. Necessary Assumptions don't simply help the argument, and they certainly don't bring new information to the table, as Strengthen questions and Sufficient Assumption questions do.

Necessary Assumptions are things we already know to be true based upon the stimulus.



Necessary Assumption Questions are Really a Specific Type of Must Be True Question

In all the LSAT materials I've looked at (and I've looked at quite a few), the authors place Necessary Assumption questions in a separate category from Must Be True questions.

In fact, the negation test described above works precisely because Necessary Assumption questions are a specific type of Must Be True question. I proved it to you above when I plucked key words from Necessary Assumption question stems: "depends upon," "requires," and "assumes." Something required to be true in order for the argument to work is something that must be true for it to work.

We could easily take any Necessary Assumption question, remove its question stem, and replace it with a Must Be True question stem, such as the following:

If all of the statements above are true, which one of the following must also be true?

The Necessary Assumption question's credited response would answer this question as well because the necessary assumption must be true if we assume the argument is valid. The important thing to keep in mind is that Necessary Assumption questions are asking you for information that needs to be the case in order for the argument to work. Must Be True questions are asking for something, anything, that has to be true based on the information in the stimulus.



Why Does the LSAT Even Have Necessary Assumption Questions?

Why not just ask Must Be True questions all the time? Why does LSAC even bother with these? What makes them different from Must Be True questions?


-Must Be True questions often involve connecting a few different pieces of information from the stimulus.

(See PrepTest 29, Section 4, Question 23, which I explained a bit here under "05/22/2009" - p42 in Next 10, or see PrepTest 33, Section 3, Question 8 - p170 in Next 10.)


-Must Be True questions often involve formal logic and are simply fact sets, rather than arguments.

(See PrepTest 30, Section 2, Question 18 - p59 in Next 10, or see PrepTest 32, Section 1, Question 7 - p120 in Next 10).


In short, they require you to make various types of connections between different pieces of information in the stimulus.

Necessary Assumption questions, on the other hand, ask for a more specific type of information that must be true. They ask for something that must be true in order for the argument itself to be valid.



Examples:

By this point, you're probably foaming at the mouth for some examples of necessary assumption questions, so I've some picked out for you:

Common Necessary Assumption Question Pattern #1
PrepTest 30 (December 1999), Section 2, Questions 15 and 22 (pages 58 and 60 in Next 10, respectively)

In each of these questions, the stimulus' argument makes the claim only one thingneeds to be true for something to occur. For each of these questions, the correct answer dismisses a potential problem that might otherwise prevent the conclusion from logically following.

Common Necessary Assumption Question Pattern #2
PrepTest 37 (June 2002), Section 4, Questions 15 and 19 (pages 312 and 313 in Next 10, respectively)

In each of these questions, the stimulus' argument mentions something new in the conclusion that was never mentioned in the evidence. They also mention something in the evidence that was never mentioned in the conclusion. As such, the new thing in the conclusion needs to be made relevant in some way for its presence in the conclusion to be justified. If it were not relevant to the evidence in any way, the argument would not be valid.


Photo by nathangibbs / CC BY-NC-SA 2.0

Necessary and Sufficient Assumptions: Arguments and Contrapositives

I spend a great deal of time talking about the difference between Necessary Assumption and Sufficient Assumption questions in the LSAT's Logical Reasoning section.

Arguments assume a link between the evidence and conclusion presented - this link can often easily be framed as a conditional statement.

Because the contrapositive of this statement is simply a rewording of the argument itself, the contrapositive of that statement is both necessary and sufficient for that argument to work.

As such, it can serve as the correct answer to both Necessary Assumption and Sufficient Assumption questions.

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Necessary Assumption
Let's start with the fact that the contrapositive of an argument's evidence-conclusion link can serve as a necessary assumption.

I mean that if X -> Y is an argument, then NOT Y -> NOT X is a necessary assumption (an assumption required) for that argument to be valid.

After all, if the contrapositive were negated, then the original statement would not be valid either, and the argument wouldn't be valid. As such, the original statement requires the contrapositive to be true as well.

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Sufficient Assumption

Additionally, the contrapositive of an argument's evidence-conclusion link can serve as a sufficient assumption.

I mean that if X -> Y is an argument, then NOT Y -> NOT X is an assumption that is sufficient for the argument to be valid. What I mean is that if we're told, as new information, that NOT Y -> NOT X is valid, it must be the case that the argument itself (X -> Y) is also valid. This is because if the contrapositive of a statement is valid, then the original must also be valid, since they're logically equivalent.

This is all a bit abstract, but let's look at it with a couple of examples from real LSAT questions:

Necessary Assumption example:

(Please see PrepTest 36 (December 2001 LSAT), Section 3, Question 16 - page 275 in Next 10)

In this argument, the stimulus tells us (paraphrased):

Because reptiles can't make big behavioral changes when the environmental changes a lot, reptiles aren't capable of engaging in advanced thought

In shorthand, the argument is saying:

NOT capable of big behavior changes with environmental changes -> Not capable of complex thought

The contrapositive of this statement would be something like:

Capable of complex thought -> capable of big behavioral changes with environmental changes

In other words:

If an animal is capable of complex thought, then it must be capable of making big behavioral changes as the environment goes through big changes.

Choice D of this question pretty much says just that.

Again, if an original conditional statement that forms the core of an argument is considered to be true, then it is required that its contrapositive also be true in order for that argument to work.



Sufficient Assumption example:

(Please see PrepTest 36 (December 2001 LSAT), Section 1, Question 26 - page 261 in Next 10)

In this argument, the stimulus tells us (paraphrased):

Because Vermeer used expensive props, it must not be due to a scarcity of props that he kept using the same props over and over.

In shorthand, the argument is saying:

$ props -> NOT due to small # of props that V kept reusing them

The contrapositive of this statement would be something like:

If it were due to a small # of props that V kept reusing them, then NOT $ props.

In other words:

If it were due to a small number of props that Vermeer kept reusing the same ones, then he wouldn't have been using expensive props in the first place.

Choice E of this question pretty much says just that.

Again, if we're told, as new information in an answer choice, that the contrapositive of the argument is guaranteed to be true (or is "assumed"), then the original version of that conditional statement (the one in the argument) must also be true, and the argument is valid.

Photo by mitopencourseware

LSAT Logical Reasoning Solutions PDF

I've written explanations for over 1,000 LSAT questions.

You can get the full LSAT PrepTest explanations for TONS of exams HERE.

LSAT Logic and the Velocity of an Unladen Swallow

In the movie Monty Python and the Holy Grail, there's a scene during Arthur's quest in which he encounters a bridge-keeper.

The bridge-keeper asks him, among other things, "what is the airspeed velocity of an unladen swallow?"

Bridge-keeper: Stop! What is your name?
King Arthur: It is Arthur, King of the Britons.
Bridge-keeper: What is your quest?
King Arthur: To seek the Holy Grail.
Bridge-keeper: What is the air-speed velocity of an unladen swallow?
King Arthur: What do you mean? An African or European swallow?
Bridge-keeper: What? I don't know that! [falls into abyss]
Sir Bedemir: How do know so much about swallows?
King Arthur: Well, you have to know these things when you're a king, you know.

Now, this is funny, but why am I talking about it?

Arthur's response is an interesting argumentative technique, and Bedemir commits a logical fallacy. Both of their responses are related to types of reasoning we see on the LSAT.

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Rather than attempt to answer the question or admit that he doesn't know the answer, Arthur simply responds with a question of his own. The bridge-keeper happens to be shocked by the question and doesn't know how to deal with it.

Arthur's response doesn't actually demonstrate any knowledge related to the velocity of unladen swallows at all, other than to suggest that perhaps he knows that the velocities of African and European swallows differ.

Bedemir is far more impressed with Arthur's response than he should be. He improperly assumes that it indicates Arthur knows something significant about the unladen swallows' airspeed velocity.

Arthur's response serves as irrelevant evidence when it comes to supporting the conclusion that he knows a great deal about swallows.

In order to properly conclude that Arthur knows something about the velocity of unladen swallows, we'd have to actually hear him say something related to their actual speed. Even if we didn't hear a firm number (such as "20 kilometers per hour") the response that it's "the same as that of a 10-year-old child riding a bicycle" would serve as much firmer evidence than what Arthur asked. (These guys did a good job of suggesting they know what they're talking about.)

See PrepTest 36 (December 2001 LSAT), Section 1, Question 12, page 257 in Next 10) for an example of an actual LSAT question where the evidence provided gives us little reason to support the conclusion.