Flaw Questions

“Flaw” type questions come in three basic forms–assumptions, logical errors, and fallacies. Doing well on flaw questions means doing well on each of these three very different challenges.


Assumptions are easiest for people with no special training in logic. It is easy to spot an assumption type answer, since  it tends to start with a phrase like “fails to consider that” or “takes for granted that.” In a typical assumption scenario, the answer choice will provide a new fact that would make a big difference to the argument. You don’t need to be a logic whiz to figure out how that new fact might change things. Since each assumption-type answer is unique to the facts in that particular argument, there is no easy way to train up to do better on assumption answers.

Logical Errors

Logical errors, by contrast, do not involve new facts. They are technically known as “formal fallacies,” which means they are wrong because of the “form” of the argument. Any “formal fallacy” can be reduced to symbolic logic so that the actual terms under discussion no longer matter. A stimulus that says “Albion is in Britain” can be rewritten as “A->B.” In a “formal fallacy,” it doesn’t matter whether “B” stands for “Britain” or “Botswana.” For example, if I say “I am in Britain, therefore I am in Albion,” I have committed the logical error that PowerScore refers to as a “mistaken reversal.” To do well on this type of flaw question, you need to do well on conditional logic as a whole. I am working on a flashcard deck for logical errors.

  • Logical error flashcards

The third type of flaw is a specialized version of logical errors that cannot be reduced to symbolic logic. These “informal fallacies” involve a host of tricks and traps for the unwary. Unscrupulous people have been using these fallacies to dupe people for so many centuries that most of them have Latin names. These Latin names never appear on the LSAT, which adds an unintended degree of difficulty to the test. The LSAT answer choices that describe these informal fallacies can be more bewildering than Latin, especially to people who have some familiarity with the traditional names. To address this problem, I am working on two sets of informal fallacy flash cards–one that identifies all the most common and/or recent fallacies by their Wikipedia names, and another which then connects those names to wording that mimics the LSAT answer choices.

  • List of fallacies
  • Fallacy flashcards
  • Flaw answer choices

Informal Fallacy Flashcards

[qwiz] [i]

Informal Fallacies: This quiz identifies all the informal fallacies in 10 Actual Official LSAT Preptests Volume V. Since many fallacies have more than one name, we have chosen the name used by Wikipedia for each fallacy.

[q multiple_choice=”true”] presents a situation in which only limited alternatives are considered, when in fact there is at least one additional option.

[c]  Sampling bias

[f] No, that would involve some kind of survey error.

[c] Begging the question

[f] No, that would mean assuming what you are trying to prove.

[c*] False dilemma

[f] Good! 

[q multiple_choice=”true”]  infers that something is true of the whole from the fact that it is true of some (or even every) part of the whole

[c*] Fallacy of Composition

[f] Good!

[c] Argument from ignorance

[f] No, that would mean using a lack of proof as a way of proving something.

[c] May/Must Fallacy

[f] Wikipedia doesn’t know about this one–it is the error of saying something must be true just because it might be true.




The “Roll the Dice” Flaw

“Find the flaw” LSAT questions are both common and difficult. There are a lot of fallacies, and some of them are quite subtle.  The answer choices use “LSAT jargon” to describe each fallacy, not textbook Latin. That means you have to know the fallacy and the special LSAT terminology for it to answer the question with speed and confidence.

I recently ran across a “find the flaw” question that totally stumped me. I guessed one answer (with no confidence) on a timed test, then came back to blind review and picked another answer–still without any certainty. Both my choices turned out to be wrong, so I looked up the answer and promised to write a blog post about it. (I recommend this same procedure to students who want a 99th percentile score–you haven’t really mastered a question until you either know you got it right  or you write an essay about why you got it wrong.)

The question I had trouble with was PrepTest 65, Secton 4, #26. I won’t violate copyright by printing it here, so here’s a new problem with the same features. (If you own “10 Actual, Official LSAT PrepTests Volume V” you can find the actual question on page 143.

Nikola Tesla Magnet School accepts only the brightest students in our metropolitan region, so it boasts the best science club in the entire Tri-State Area. The best science club is most likely to win the annual robotics competition, so the Nikola Tesla Magnet School will almost certainly bring home the trophy this year.

I read this stimulus and immediately zeroed in on the difference between the best individual students and the best overall team. That’s such a common fallacy that it has a Latin name (“modo hoc“), although it’s not clear whether it applies in this case. But I never got that far because that wasn’t one of my answer choices. Here’s what was offered on the LSAT:

(A) presumes, without presenting relevant evidence, that an entity can be distinguished as the best only on the basis of competition.

(B) predicts the success of an entity on the basis of features that are not relevant to the quality of that entity.

(C) predicts the outcome of a competition merely on the basis of a comparison between the parties in that competition.

(D) presumes, without providing warrant, that if an entity is the best among its competitors, then each individual part of that entity must also be the best.

(E) concludes that because an event is the most likely of a set of possible events, that event is more likely to occur than not.

I was trying so hard to find a composition fallacy (that’s modo hoc for you Latin lovers) that I really wanted D to be correct, but it just wouldn’t work. I wound up picking C, then switched to A. B never appealed to me, and I never really understood what E was all about.

That was a mistake.

E is all about rolling dice. If I roll a pair of dice, seven is the most likely outcome. There are six out of thirty-six chances that I will roll a seven, making it more likely than any other roll (there’s a 1/36 chance of rolling two or twelve, a 2/36 chance of rolling three or eleven, etc., etc.). But just because seven is the single most likely roll, it’s not more likely to occur than not. I only roll a seven one out of six times. I’d have to roll it every other time (plus some) for it to be “more likely to occur than not.”

Most likely, but not more likely than not

That was my error. A science club may be “more likely” to win than any other club in the city, but that doesn’t mean it will “probably” win.

I’ve searched the Internet for the Latin name of this fallacy, and haven’t found it yet. You Latin buffs may refer to it as “alea jacta est.” The rest of us can just call it the “roll of the dice fallacy.”

Find the Flaw: A Difficult But Useful Skill

Some things you do to prepare for the LSAT are a waste of time as far as the rest of your life in concerned. Your ability to recognize a “parallel reasoning” question and skip over it until the end of the section is not going to help you be a better lawyer. But that is not true of all LSAT preparation. At least one area where you need to invest some significant time will serve you well throughout your life and legal career. That area is the “find the flaw” logical reasoning question type.

Logicians call these “flaws” fallacies, and diagnose them as carefully as doctors do diseases. If you take an old-fashioned logic class in an academic setting, you may still be expected to learn their Latin names, such as argumentum ad hominem, argumentum ad baculum, argumentum ad misericordiam, etc.

It used to be you couldn’t be a lawyer without knowing quite a bit of Latin, but aspiring lawyers aren’t expected to learn Latin anymore. That’s why the LSAT doesn’t give you Latin names in the answer choices. Unfortunately, the answer choices they do provide might as well be in Latin for all the good they do the brand-new test-taker. “Find the flaw” answer choices are worded in what I call “LSAT jargon,” a unique dialect found nowhere else on earth.

It isn’t that “find the flaw” answer choices aren’t in English, or that they don’t actually mean something. The problem is that an intelligent person can read the answer twelve times in a row and still not get what the test-writer is saying. Sometimes the only way to figure out what these answer choices mean is to look at the answer in the back of the book. Only after you see that “E” is the right answer will the fog clear and understanding set in. But by that time, you’ve already circled “C,” changed it to “A,” and beaten your head against a wall.

That’s the bad news. The good news is that LSAT jargon is no harder to learn than Latin, and the effort you make on this one question type will serve you the rest of your life. You will need to spot flawed reasoning in every contract you review, will you draft, deposition you take, or witness you put on the stand. On the LSAT, you have more than a minute to figure out a “find the flaw” problem. When your opponent is making her pitch to the jury, you have scant seconds; and when you explain your objection to the judge, you need to speak English, not Latin.

You might impress a jury by saying, “Your Honor, the counsel for the prosecution has committed a post hoc, ergo propter hoc fallacy,” but if the judge got his law degree in the last twenty years, you’re more likely to annoy him than persuade him. Try saying, “The State has confused a cause with a correlation, your Honor. Just because one thing happens after another thing does not mean it was caused by that other thing.” That might get your objection sustained and your client out of jail! And when your grateful client hugs you and hands you a check, you can say, “Don’t thank me–thank the LSAT!”