Flaw Answer Choice Flashcards

[qwiz] [h] Flaw Answer Choices

[i] The LSAT requires no formal training in logic. This is usually an advantage, but creates some challenges when it comes to identifying logic errors and informal fallacies. A person who is familiar with the traditional names for fallacies may instantly identify a particular flaw as a case of “denying the antecedent” yet still be bewildered by the answer choices that are presented. These flashcards matches examples of actual LSAT answer choices (carefully paraphrased, out of respect for copyright) to the Wikipedia names for the respective fallacy.

 

[q multiple_choice=”true”] fails to consider that there may be other necessary conditions for the result beyond the specific condition that was identified

 

[c*] Affirming the Consequent

[f] Correct!

[c] May/Must Fallacy

[f] Not the best choice–but it has been credited as a correct answer for this situation.

[/qwiz]

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

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
Fallacies

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.

[/qwiz]

 

 

Eliminating Wrong Answers

I’m always looking for objective ways to eliminate wrong answers. Here’s a tip from “bswise2″ I just read on the 7Sage.com forum:

In an “assumption” question (whether necessary or sufficient), read the conclusion and look for any new terms that do not appear elsewhere in the stimulus. The right answer MUST contain that term. Eliminate all that do not.

Logic Games: Must Be Easy

I have been struggling to explain “must be” questions to my logic games students. Sometimes they are super easy. Sometimes they are super hard. In the first case, you can read the correct answer right off your sketch. In the second case, the only way to solve one “must be true” question is to find four “could be false” solutions–and my students who are having trouble with logic games in general get tied up in knots trying to figure that out.

i have also been struggling with helping students know when to stop working out initial inferences. They know they are supposed to draw a sketch, write down the rules, and start looking for the obvious implications of those rules, but how do you know when you’re done?

As things would happen, it turns out that there is one simple answer to both of these difficult problems. I call it the “must be easy” rule.

Most logic game questions fall into one of two categories: “must be” and “could be” questions. “Which of the following must be true” is an obvious “must be” question, and so is “which of the following cannot be true.” In theory, the answer to “must be” question is something you might add to your logic game sketch. Thus, if question 3 asks, “Which of the following cannot occur on Tuesday,” you should be able to pencil in a “Not X” underneath Tuesday on your sketch.

A “must be easy” question is one where the answer is already penciled into your sketch. The only way to tell whether a “must be” question is a “must be easy” question is to look at it. It should take about three seconds per answer to decide whether you have already deduced the answer to this question. If you have, you’re done. That was fast–and easy!

If you haven’t already found the answer to your “must be” question, take another look at it. Is it a “focused” question? Logic game questions that ask about  a specific entity or slot are “focused,” a “must be focused” question is practically shouting at you, “Hey! There’s something about this slot or entity that you haven’t figured out yet.” If so, now is the time to think it through and add it to your sketch.

If it’s not easy, and it’s not focused, it may still be important–especially if it comes early in the game. I have seen this on several grouping games that have “/A->B” rules on grouping games.  (I have written about the importance of such rules here.) Take a moment to ask whether this is a “must be important” question.

If it isn’t easy, and it isn’t focused, and you can’t quickly think of any less-common but very-important deductions you should be making, it “must be hard.” That is a subject for another day. (Add hyperlink HERE when that day comes…)

Here are some examples from “10 Actual, Official LSAT Preptests Volume V.”

Preptest 62, Game 1, Question 4: if you already noticed that both gas and satellite must both fall on the last three days, Question 4 is a “must be easy” question. If not, now’s the time to ask, “What do I know about these days?”

Preptest 62, Game 2, Question 8: if you realized that “/P->O” means you have to have either purple or orange in every window, this “must be easy.” If not, this is neither easy nor focused–but it’s a critical inference. If you don’t understand that every window must have either purple or orange in it, this is one of the two hardest logic games in recent years. If you do see that the “/P->O” rule means “P or O” in every window, then it’s pretty straightforward.

Preptest 63, Game 1, Question 2: if you realized that “/H->P” means “H or P” on each court, including the appellate court which only has three slots and one is already filled, then this “must be easy.” If not, this is neither easy nor focused–but it is important! Question 3 and 4 both depend on exactly the same inference.

Preptest 63, Game 2, Question 7: if you noticed that W can’t come last and T comes before W so T can’t come next to last, then this was easy. If you notice that “at least two of the members dive after so-and-so,” then this is focused. The question is asking, “Who can’t dive last or next-to-last?”

Preptest 63, Game 3, Question 12: if you always knock out a whole staircase of entities at either end of a sequence that includes an ordered chain (“A…B…C” means B and C are out on the first day, and C is out on the second day, and A and B are out on the last day, and A is out on the next-to-last day), then this question “must be easy.” If you don’t, then it focuses your attention on Thursday.