Articles published in Logical Reasoning

LOGICAL REASONING: Beware of Sliding Scales that Don’t Exist

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Penguin Boxer

To make up for lack of flight ability, Pen Gwynn (pictured) took up heavyweight boxing

Inference questions in Logical Reasoning ask you to infer what must be true. This means that the answer choice you pick shouldn’t stretch beyond the scope of the text in the stimulus. You want to stay as close to the text as possible, which is why we say things like, “Be literal!” and “Make only baby inferences” (maybe that second one is just me).

Here’s an example of one way wrong answer choices try to trick you. The stimulus will provide statements in black and white—light switches, not dimmers. For example, “all artists are attentive to detail,” “no kangaroos are stupid,” or “most birds fly.” (Notice that even this third example offers a trigger, not a sliding scale. They either fly, or they don’t.)

Sometimes on these kinds of questions, you’ll find answer choices that create issues of degree that don’t exist in the argument. For example, wrong answer choices corresponding to these examples, respectively, might say that artists are more attentive to detail if they eat bacon for breakfast, or that large kangaroos are stupider than small one, or that birds fly better if they are flying with other birds. All three of these are examples of false inferences from the statements above that you can recognize because they create issues of degree that do not exist in the argument.

You can think of this kind of wrong answer as a dimmer (when the argument is a clapper), or a sliding scale, when the argument discusses no such scale.

To try the kind of problem that I’m talking about, check out PT43, S2, Q22 and PT41, S1, W2, and then check out our forum explanations of each.

LOGICAL REASONING: The Conclusion Cap

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When you’re looking for a necessary assumption, remember that you’re looking for what must be true, and what must be true doesn’t necessarily “fill the

Necessary vs Sufficient

Barry's suit & briefcase disguise: necessary, but not sufficient

whole gap,” as we say. It could be a small piece of the puzzle, but a critical one. Imagine a bridge supported by several buttresses, each of which is necessary (you knock it down and the bridge falls) even though it could never support the bridge on its own. Therefore, the buttresses are necessary, but certainly not sufficient, for supporting the bridge.

For these reasons, you generally want to be wary of answer choices that seem sweeping—words like “always” and “never” are tip-offs. (This isn’t to say those answers are never right, though. If the argument is extreme, there can be a necessary assumption that is, too.)

A good rule of thumb is that the conclusion caps how “strong” the necessary assumption can be. If the conclusion is on the milder side of the spectrum

—“Jenn will probably choose cake over pie” or “Jim is likely to find the suit distasteful”—it wouldn’t make sense to choose answers that read, respectively, “Jenn will always choose cake over pie” and “Jim will definitely find the suit distasteful.” These wrong answers push the arguments beyond their scope, which has already been set.

This isn’t a new concept but simply another way of thinking about the same old idea. The conclusion caps off the argument, and at the cap, it stops assuming.

Logical Reasoning: What the _________?

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Dog

Don't let your imagination run wild while filling in the blank

Fill-in-the-blank-line-at-the-end-of-the-argument questions have been known as Inference questions delivered in a fancy package. “These,” I tell students, “ask you to find a conclusion, but don’t start thinking creatively. Your task is still to find an answer that must be true.” This is easy to grasp, since something you can infer from a premise could also be called a valid conclusion. So that was that.

But there’s a different flavor of fill-in-the-blank questions creeping into the LSAT from time-to-time! For example, on PrepTest 63, Section 1, Question 1 and PrepTest 65, Section 4, Question 15, you’re asked to fill in the blank… with something that will strengthen the argument’s conclusion. “Wait!” you’re thinking, “We don’t strengthen conclusions on Inference questions…” That’s right. In fact, on Inference questions, there is no conclusion in the stimulus–your answer could be considered the conclusion. We can think of PT63, S1, Q1 and it’s comrade on PT65, therefore, as Strengthen questions–you want to make the conclusion inferable.
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LSAT Logical Reasoning: Styrofoam Arguments

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NoahAs you can imagine, being an LSAT teacher carries great risks. What used to be good old fights about doing the dishes are now fights about doing the dishes AND the assumptions underneath the statement “When you leave the dishes on the sink, it makes me feel like you’re an a@#$&@(#!”

But, enough about dishes we have to wash, let’s talk about disposable dishes! Yesterday I went and bought a shredded chicken burrito (half-and-half spicy/mild) at Santiago’s, my second favorite Mexican restaurant. I also picked up a frosty soda to wash it down (“pop” for Midwesterners). It arrived in a lovely Styrofoam cup. Later, while waiting in line (“on line” for New Yorkers), I satisfied my need to be constantly doing something (“ADHD” for you youngins) by reading the cup. I faced these two statements:
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Logical Reasoning: A Tricky Breed of Principle Example Questions (Illustrations of Illustrations)

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Principle Example questions on the logical reasoning section ask you to find an illustration (or example) of a principle given to you in the stimulus. The most straightforward of these provide an outright principle (generally stated) followed by five answer choices describing specific situations. For example, one might look like this:

Inception

It's an illustration within an illustration

‘Tis better to give than to receive. 

Which of the following best illustrates the principle stated above? 

(A) It is better for Jeremy to give his dad an HDTV than to give his mom a necklace. 

(B) It is better for Jeremy to get a motorcycle from his dad than from his mom. 

(C) It is better for Jeremy to give his sister the iPad than to keep it for himself. 

(D) It is better for Jeremy’s sister to give the iPad to Jeremy than to give it to charity. 

(E) It is better for Jeremy to give his girlfriend a Dr. Seuss book than to receive one from his sister. 
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The Morbid Flaws

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Some people have trouble with flaw questions on the LSAT because there are two ways the answer choices can be worded. One just points out the assumption by asking what the argument “takes for granted.” The other points out the assumption, too, but in a more indirect way; it tells you something the argument isn’t considering by making the assumption:

The argument fails to consider that…

Or

The argument ignores the possibility that…

When I teach flaw questions, there are a couple of morbid examples I like to use to illustrate the difference. So apologies in advance for being a Debbie Downer, but I like to think the morbidity of these makes them more memorable. Here they are, the Morbid Flaws. Read more

The Necessary Alarm Clock

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The terms “necessary” and “sufficient” get thrown around a lot in the LSAT world these days. We at Manhattan LSAT use them to distinguish between two different kinds of assumption questions. They come up on the test in answer choices (for example, “The argument mistakes a necessary condition for a sufficient condition”). And usually by the fourth session of a course, students start making jokes like, “I had half a sandwich earlier, which was necessary, but not sufficient.” We all pretend not to love the joke.

But what do they mean? One of my favorite analogies for explaining the basic difference between necessary and sufficient is the alarm clock. We’ll call it the Necessary Alarm Clock.

alarm clock

Say I have a very hard time waking up. I’m a sad, awful person who hates morning, sunlight, and everything to do with happiness. I so dread being awake, in fact, that in order for me to get up in the morning, eight things need to happen:

1. My alarm clock goes off.
2. The smell of bacon drifts into my room.
3. I have dreamt of lilies and puppies.
4. Speaking of puppies, my dog is licking my face.
5. A marching band passes.
6. It’s not a Monday.
7. I am not hungover.
8. It is 72 degrees in my bedroom.

Again, in order to wake up, every single one of these things must occur.

So what is sufficient for me to wake up? 1-4? 5-8? 1, only? None of these. The occurrence of 1-8 is sufficient for me to wake up, and 1-8 only. Could we say, then, that 1-8 is also necessary for me to wake up? Sure! Each of these has to happen; that means they are all necessary.

How about my alarm clock going off? Is that sufficient for me to drag my caboose outta bed? No. 2-8 still has to occur. But is it necessary? To answer that question, we ask what would happen if it DIDN’T go off. If it didn’t go off, I’m still snoozing. So, yes, it’s necessary.

Finally, suppose 1-8 occurred, plus there were fourteen cheerleaders practicing in my kitchen. Would I wake up? Of course I would. The sum total of 1-8 plus the cheerleaders is sufficient to get me out of bed. But is the sum total of 1-8 plus the cheerleaders necessary to get me out of bed? No. The cheerleaders can be disposed of.

Yes, I wrote this post just to be able to close with that sentence.

Logical Reasoning And Rick Santorum

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Rick Santorum

Rick Santorum sure has made some controversial remarks lately. But are they logically sound? Regardless of your political leaning, it pays to know how to evaluate the pieces and soundness of an argument. For this week’s post, I’ve plucked a few Santorum gems to help you review logical reasoning strategy. Can you identify the question types, below? Better yet, can you answer them? Answers after the jump! Read more

One of the Hardest LSAT Questions – @!#$%@# Dioxin!

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Like snowflakes of intellectual pain, the hardest LSAT question is different for each and every one of us – it’s up to us to look into our hearts and find the question that is burning a hole through an artery. For me, that was PT45, S1, Q12 – the dioxin question. Oh how we fought, oh how we struggled!

Let me walk you through our relationship.

The conclusion of the argument is that, as opposed to what most people are thinking, dioxin released from a mill does NOT cause fish to have abnormal hormone levels. Why? Two premises are given to support this – and here’s where we had our first fight L: dioxin decomposes quite slowly and when the mill shuts down, the fishy hormone levels quickly return to normal.

At this point, me and question 12 were still on speaking terms, but when I looked at her answer choices, oh the pain! The correct answer – the one that most weakens the argument – states that dioxin actually is washed away pretty quickly from the mill area. Sounds painless enough – until you think about it! How does that weaken that argument? I was lost. Read more

LSAT Vocabulary

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//lsatblog.blogspot.com/2010/01/logical-reasoning-vocabulary-words.html

I just saw a good blog post listing vocabulary words that you should have under your belt for the LSAT.   Take a look and see if you really know all of them.  Thanks for the list, Steve!