Logical Reasoning

PT104 · S1 · Q23 Research indicates that 90 percent

A free, expert breakdown of this official LSAT Logical Reasoning question.

  • Save & drill this skill — build targeted practice sets from questions like this one

  • Video walkthroughs — watch every question solved step by step

  • 81 official LSATs — as questions, timed sections & full-length tests

Start practicing free

Research indicates that 90 percent of extreme insomniacs consume a large amount of coffee.

Conclusion

It's quite likely that Tom is an extreme insomniac.

Evidence (since)

Tom drinks a lot of coffee, and 90% of extreme insomniacs consume large amounts of coffee.

Evaluate

This is not a great way to argue. 90% of prisoners in maximum-security prisons drink coffee every morning. I drink coffee every morning. Does that make it quite likely that I am a prisoner in a maximum-security prison?

Of course not. Just like conditional statements, "most" statements cannot be read backwards.

GIVEN - All Senators speak English. CAN INFER - Bob is a Senator. Thus, he speaks English. CAN'T INFER - Bob speaks English. Thus, he is a Senator.

GIVEN - Most Senators are men. CAN INFER - Charlie is a Senator. Thus, Charlie is probably a man. CAN'T INFER - Charlie is a man. Thus, Charlie is probably a Senator.

GIVEN - Most extreme insomniacs drink lots of coffee. CAN INFER - Tom is an extreme insomniac. Thus, it is quite likely that he drinks a lot of coffee. CAN'T INFER - Tom drinks a lot of coffee. Thus, it is quite likely that he is an extreme insomniac.

Goal

Look for an answer describing the way the author is reading this Most statement in an illegal backwards way.

Or look for an answer making the objection that . In that case, knowing that Tom is a coffee drinker would lead to the conclusion that he likely isn't an extreme insomniac.

23.

Which one of the following most accurately describes a flaw in the argument's reasoning?

  1. It fails to acknowledge the

    Doesn't Fail to Consider

    The author acknowledges this possibility by saying "Tom is quite likely an extreme insomniac". If the author had concluded, "thus Tom is definitely an extreme insomniac", then she would be failing to acknowledge that a 90% statistic (even if misread, as the author is doing) would not prove certainty.

    12% picked this

  2. It fails to consider the

    Out of Scope: causes

    Nothing in this argument is saying that anything caused something else, so we wouldn't be able to weaken the argument by bringing up alternate causes. This argument is only talking about people who are / aren't a certain thing, or who do / don't do a certain thing.

    7% picked this

  3. Correct

    It relies on evidence that

    Why this is right

    This is pointing out the fact that the statistic the author cites is useless to the argument she's trying to make. If we're saying, Tom drinks coffee. Thus he's probably an insomniac. We need to know that Most coffee drinkers are insomniacs. In order for us to assess the likelihood that Tom is an extreme insomniac, based on the fact that he drinks a lot of coffee, then we need to know, "What % of big coffee drinkers are extreme insomniacs". (Instead, the author uselessly brought up what % of extreme insomniacs are big coffee drinkers) This answer choice is just complaining that the author didn't provide us with the actual statistic that we'd need to evaluate the conclusion (or that she would need to prove the conclusion). If you want to try a similar problem, try this one.

    Skill tested: Flaw · how this choice captures the argument's function is the move to repeat next time.

    45% picked this

  4. It draws an inference about

    Wrong Flaw: not Part v. Whole

    If a flaw answer choice says the author inferred X from evidence that Y, we would ask ourselves if Y matches the Evidence and if X matches the Conclusion (or some assumption en route to the conclusion). Was the conclusion "an inference about one specific individual"? Sure, it was about Tom. Was the evidence describing only the characteristics of a class of individuals? No, not quite. First of all, there are two premises, and one of them is just about Tom (he drinks a lot of coffee). That would already make us doubt this answer. It's also tough to say that "90% of extreme insomniacs consume a large amount of coffee" is describing the characteristics of a class of individuals. It's describing a characteristic about 90% of a class of individuals. One final issue is that it's not inherently objectionable to draw an inference about a specific individual from evidence that describes the characteristics of a class. i.e., if the argument had been "All big coffee drinkers are insomniacs. Tom drinks coffee. Thus, Tom is an insomniac", that would be an airtight argument and this answer choice would still be applicable.

    30% picked this

  5. It presumes without warrant that

    Too Strong

    Too Strong: always Out of Scope: causal Nothing about this argument is causal, so the author didn't need to make any assumption about anything causing other stuff. She certainly didn't need to make any extreme assumption that drinking coffee always causes insomnia.

    6% picked this

Continue the review in LSAT Lab

Save this question, watch the video walkthrough, and drill similar questions in your LSAT Lab account.

Save and practice this skill
LSAT Lab

Turn this review into a targeted study plan.

Save this question, drill more like it, watch the video walkthrough, and track your progress in your LSAT Lab account.

Start practicing free