No LSAT Practice is Complete Without Logical Reasoning

Last week, our LSAT practice quiz dealt with logic games. Stepping up to the plate for LSAT practice this week: Logical reasoning.

LR is the most consistent section from test to test and makes up 50 percent of your LSAT score. Thus, your LSAT practice should focus largely on mastering this section. The majority of the questions revolve around only a few concepts – arguments, validity and fallacies. If you can master these concepts during LSAT practice, proficiency with most question types will follow.

Below are a couple of original LR questions. Some do not have answer choices. This is to force you to anticipate – just another form of LSAT practice.

Batter up!

Few Blueprint students have any LSAT practice experience before their first Practice Exam. For many, it is their first encounter with the test. Their first Exam scores vary widely. Although many students study for a similar number of hours, they often progress at different rates. Obviously then, logical skill and LSAT performance must be determined by genetics.

1. What are the flaws in the argument?

2. Which one of the following, if true, would most strengthen the argument?

a. Scientists have recently located the section in the brain that deals with abstract concepts and logical reasoning and found that it varies in size from person to person.

b. Many students who perform well on the LSAT have siblings who also perform well.

c. A comprehensive study of students studying for the LSAT found little correlation between number of hours spent studying and score improvement.

d. Researchers recently discovered that performance on the LSAT is completely unaffected by past exposure to logical concepts and argumentation.

e. Some students practice LSAT questions on their own before signing up for an LSAT course.

Nutritionist: Before the advent of agriculture, our ancestors ate a diet free from grains, legumes and dairy. Since they were remarkably free from Western civilization diseases such as diabetes, heart disease and even Alzheimer’s, everyone who desires optimal health should eat such a diet. Over the last century, technological developments (including sliced bread) have contributed to the proliferation of such processed foods, especially those made from grains. And as these foods became abundant and readily available, obesity and heart disease rates skyrocketed.

3. What is the main point of the argument?

4. What relationship is contained within the conclusion?

5. What is the primary error of reasoning contained within the argument?

6. Which one of the following, if true, would most undermine the conclusion?

a. In recent time, when cultures have shifted from their indigenous diets toward a more western diet, obesity and disease rates have increase dramatically.

b. Many people who eat grains, legumes and dairy don’t feel they suffer any adverse effects as a result.
c. Many foods are packaged in plastics known to leak potential toxins into the foods.

d. A research team recently discovered that only a small minority of people are actually allergic to gluten, the main protein found in most grains, or lactose, the main sugar in milk.

e. Traditionally, as populations have shifted toward a westernized diet, they have also vastly decreased their physical activity and amount of sleep.


1. Two flaws: Exclusivity, in that it ignores other options – including exposure to similar concepts in the past (logical arguments in philosophy or politics); and flawed comparison, in that you can’t compare different peoples’ LSAT practice by just the number of hours spent studying; you must consider the quality of the time spent on LSAT practice.
2. D
3. If you want optimal health, eat this diet
4. Grains/Legumes/Dairy cause disease
5. Correlation does not imply causation
6. E

Did you strike out or hit a home run? Let me know in the comments. And keep up your LSAT practice.

13 Responses

  1. Joseph says:

    I don’t see how we could logically arrive at answer D for the first question. This introduces new information which is past exposure and doesn’t seem to bridge the leap in logic. I would have thought that a more direct way in which to strengthen the leap from study hours to genetics would be the introduction of siblings.

    • Collin says:

      D does introduce new information, but it puts to rest a possible alternate cause that would doubt the author’s conclusion. If it were the case that past exposure to logical concepts affected LSAT performance, it would weaken the argument by presenting an alternate cause. By eliminating this alternate cause, answer D gives more credence to the conclusion drawn by the author (i.e. strengthening it).

      • Collin says:

        Also, “many students. . .” doesn’t mean most….”many” on the LSAT should be read as “some”. Since “some” is a pretty weak quantifier, so is “many”….meaning that answer choice B really isn’t saying all that much.

        • Nick Rey says:

          Colin is spot on.

          Also, regarding anticipating D – if you can identify the flaw in the argument as exclusivity (failing to consider option C), you should be on the lookout for any answer choice that dismisses potential alternate causes (option Cs). In other words, if we want to properly conclude that LSAT performance is determined by genetics, we need to show that it’s is not actually being determined by hidden factors, like past exposure to arguments and logic. Hence, D.

  2. Jani says:

    I got all the answers right except the second problem, #4. i dind’t really understand the question, so I put “analogy.” haha

    • Nick Rey says:

      Sorry about that; I think I may need to work on my wording a bit. The idea was to help suggest/point to the underlying causal relationship contained within the conclusion. Oftentimes students don’t see causal relationships that may be hidden in a “should” conclusion, but it is essential that to see it in order to anticipate properly.

  3. Jani says:

    Also, for the second problem, question #5, can another error of reasoning be logical force (mistaking past for present)?

    • Nick Rey says:

      Yes, it seems like it does, but in a weird way. The temporal flaw occurs when you assume that conditions in the past necessarily continue into the present (or vise versa). Here, the argument does commit a subtle temporal flaw, in that it assumes that all other important conditions did not change (or at least did not change enough to be an alternate cause of the diseases). Basically, it doesn’t address other potential factors that changed and therefore could be a cause, which points us back to the primary causal flaw. Good catch.

  4. Erika says:

    Great questions but since I’m still on Lesson 10 (in the middle of strengthen q’s hw actually) I struggled with the strengthen question. Eliminating alt causes is sort of difficult for me because I get stumped on thinking of alt causes and then I have to think that these alt causes are not occurring. Is there an easier way to eliminate those pesky answer choices besides this process?

    Also for the Nutritionist question, I thought a flaw could also be absence of evidence since they concluded that they should have an optimal diet due to the absence of Western civilization diseases?

    • Nick Rey says:

      No worries; anticipating potential alt causes can be difficult at first – keep practicing you’ll get better. Start by thoroughly breaking down the argument – identifying conclusion, premises and assumptions – and ask yourself if this argument would convince you, and if not, why not. Often the argument will suggest what you should anticipate – think of obvious areas the argument is ignoring. Many times you won’t be able to anticipate specifically what alt causes may be present, instead you should try and anticipate general categories.

      In #1, the argument concludes that LSAT performance is determined by genetics – a strong claim which excludes the possibility of any environmental influence having a larger impact than your genetics (this nature vs. nurture subtext is a common theme for the LSAT). Since the argument only talked about LSAT study time, it’s ignoring a whole class of other possible environmental influences that may be at play. So your anticipation should be Eliminating anything that could affect your LSAT score, besides genetics. D fits nicely into this category.

    • Nick Rey says:

      Also, in #2 I don’t think the argument commits the absence of evidence flaw. Absence of evidence is a flaw when the argument concludes that a claim is false just because it lacks support (literally, that an absence of evidence for a claim makes that claim false). Here the argument is using the absence of disease to support the claim that the diet is more healthy (in one case there is disease, in another there isn’t – thus the situation without disease must be healthier).

      The absence of evidence flaw would have occurred if the argument had jumped from a premise: Studies have failed to show any health benefit to diet X. To conclusion: Therefore, diet x has no health benefit. (just because we don’t have evidence for a benefit does not mean it doesn’t exist).

      Hope this helps.

  5. Jen says:

    Hm. For #1 after reading your explanation, I see why D is correct (eliminates alt. cause). But why not C? The argument does assume that number of hours and the LSAT score improvements are unrelated, and C does seem to strengthen that assumption by claiming that study hours are uncorrelated with the score improvement.

    • Nick Rey says:

      Great question Jen. I have a couple of thoughts – first, C is basically a restatement of a premise in the stimulus (kids study same hours but have diff. results) – sure it’s a little stronger, but it’s not really adding much to the argument.

      And perhaps more importantly, it’s not strengthening the conclusion of the argument. We want an answer that makes the conclusion more likely – something that will help establish that LSAT is determined by genetics. This answer doesn’t tell us enough – even if study time doesn’t correlate with improvements, is that because of genetics? Or is it because of poor study habits? Perhaps some people are taking Blueprint classes while others are stuck with inferior methods? Any number of possibilities would fit with C and since C doesn’t commit to any of them, since it doesn’t isolate genetics as the important factor, it’s not strengthening the conclusion.

      To avoid tricky answers like C, remember to anticipate. Notice the form of the argument, and any flaws or holes in the argument, then seek to fix them. Here the flaw was exclusivity, and only one answer addresses it.

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