Assumption vs. Strengthen Critical Reasoning Questions: What’s the Difference?

GMATI had a discussion with a tutoring student the other day about the distinction between Assumption and Strengthen questions in the Critical Reasoning section. The two categories feel similar, after all. They are different, however, and the difference, as with most Critical Reasoning questions, lies mainly in the texture of the language that would be most appropriate for a correct answer in either category.

To illustrate, let’s take a simple argument: Dave opens a coffee shop in Veritasville called Dave’s Blends. According to surveys, Dave’s Blends has the best tasting coffee in the city. Therefore, Dave’s Blends will garner at least 50% the local market.

First, imagine that this is a simple Strengthen question. In order to strengthen this somewhat fanciful conclusion, we’re going to want strong language. For example: Virtually all coffee drinkers in Veritasville buy coffee daily from Dave’s. That’s a pretty good strengthener. The statement increases the likelihood that Dave’s Blends will dominate the local market. But an answer choice such as, “Some people buy coffee at Dave’s,” would be a lousy choice, as the fact that Dave’s has at least one customer is hardly a compelling reason to conclude that it will get to at least a 50% market share.

Now imagine that we take the same argument and make it an Assumption question. The first aforementioned answer choice is now much less appealing. Can we really assume that virtually everyone in town will get their coffee at Dave’s? Not really. If Dave’s has 51% of the market share, it doesn’t mean that virtually everyone gets their coffee there. But now consider the second answer choice – if we’re concluding that Dave’s will get at least half of the local market, we are assuming that some people will purchase coffee there, so now this would be a good answer.

The difference is that in a Strengthen question, we’re looking for new information that will make the conclusion more likely. In an Assumption question, we’re looking for what is true based on the conclusion.  Put another way, strong language (“virtually everyone”) is often desirable in a Strengthen question, whereas softer language (“some people”) is usually more desirable in an Assumption question.

Let’s see this in action with a GMAT practice question:

For most people, the left half of the brain controls linguistic capabilities, but some people have their language centers in the right half. When a language center of the brain is damaged, for example by a stroke, linguistic capabilities are impaired in some way. Therefore, people who have suffered a serious stroke on the left side of the brain without suffering any such impairment must have their language centers in the right half. 

Which of the following is an assumption on which the reasoning in the argument above depends?

(A) No part of a person’s brain that is damaged by a stroke ever recovers.
(B) Impairment of linguistic capabilities does not occur in people who have not suffered any damage to any language center of the brain.
(C) Strokes tend to impair linguistic capabilities more severely than does any other cause of damage to language centers in the brain.
(D) If there are language centers on the left side of the brain, any serious stroke affecting that side of the brain damages at least one of them.
(E) It is impossible to determine which side of the brain contains a person’s language centers if the person has not suffered damage to either side of the brain.

First, let’s break this argument down:

Conclusion: People who suffer a stroke on the left side of the brain and don’t’ suffer language impairment have language centers in the right half of the brain.

Premises: Most people have language centers on the left side of the brain, while some have them on the right. Damage impairs linguistic capabilities.

This is an Assumption question, so we’re looking for what is be true based on the way the premises lead to the conclusion. Put another way, softer language might be preferable here. Now let’s examine each of the answer choices:

(A) Notice the extreme language, “No part…ever recovers“. Can we really assume that? Of course not – some portion might recover. No good.

(B) We don’t know this. Imagine someone has a part of his or her brain removed and this part of the brain doesn’t contain a language center. Surely we can’t assume that this person will have no language impairment at all. No good.

(C) Again, notice the extreme language, “…more severely than other cause. Can we assume that a stroke is worse than every other kind of brain trauma? Of course not. No good.

(D) Now we’re talking. Here, we are given more generous language: damages at least one of them. “At least one” is a pretty low bar. Remember that the conclusion is that someone who suffers a left-brain stroke and doesn’t have language impairment must have language centers on the right side. Well, that only makes sense if there’s some damage somewhere on the left. This answer choice looks good.

(E) Notice again the extreme language, “…it is impossible“. There may be some other way to assess where the language centers are. No good.

Therefore, our answer is D.

Takeaway: Strengthen questions and Assumption questions are not identical. In a Strengthen question, we want a strong answer choice that will make a conclusion more likely. In an Assumption question we want a soft answer that is indisputable based on how the premises lead to the conclusion. Attention to details in the language (some vs. most vs. all) is the key.

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By David Goldstein, a Veritas Prep GMAT instructor based in Boston. You can find more articles written by him here.

Quarter Wit, Quarter Wisdom: How to Negate Assumption Answer Choices on the GMAT

Quarter Wit, Quarter WisdomMost GMAT test-takers come across the Assumption Negation Technique at some point in their preparation. It is one of the most effective techniques for assumption questions (which are usually fairly difficult) if you learn to apply it successfully.

We already know that many sentences are invalidated by negating the verb of the dominant clause. For example:

There has been a corresponding increase in the number of professional companies devoted to other performing arts.

becomes

There has not been a corresponding increase in the number of professional companies devoted to other performing arts.

Recently, we got a query on how to negate various modifiers such as “most” and “a majority”. So today, we will examine how to negate the most popular modifiers we come across:

  • All -> Not all
  • Everything -> Not everything
  • Always -> Not always
  • Some -> None
  • Most -> Half or less than half
  • Majority -> Half or less than half
  • Many -> Not many
  • Less than -> Equal to or more than
  • Element A -> Not element A
  • None ->  Some
  • Never ->  Sometimes

Let’s take a look at some examples with these determiners:

1) “All of the 70 professional opera companies are commercially viable options.”
This becomes, “Not all of the 70 professional opera companies are commercially viable options.”

2) “There were fewer than 45 professional opera companies that had been active 30 years ago and that ceased operations during the last 30 years.”
This becomes, “There were 45 or more professional opera companies that had been active 30 years ago and that ceased operations during the last 30 years.”

3) “No one who is feeling isolated can feel happy.”
This becomes, “Some who are feeling isolated can feel happy.”

4) “Anyone who is able to trust other people has a meaningful emotional connection to at least one other human being.”
This becomes, “Not everyone who is able to trust other people has a meaningful emotional connection to at least one other human being.”

5) “The 45 most recently founded opera companies were all established as a result of enthusiasm on the part of a potential audience.”
This becomes, “The 45 most recently founded opera companies were not all established as a result of enthusiasm on the part of a potential audience.”

6) “Many of the vehicles that were ticketed for exceeding the speed limit were ticketed more than once in the time period covered by the report.”
This becomes, “Not many of the vehicles that were ticketed for exceeding the speed limit were ticketed more than once in the time period covered by the report.”

7) “The birds of prey capture and kill every single Spotted Mole that comes above ground.”
This becomes, “Not every single Spotted Mole that comes above ground is captured and killed by the birds of prey.”

8) “At least some people who do not feel isolated are happy.”
This becomes, “No people who do not feel isolated are happy.”

9) “Some land-based mammals active in this region, such as fox, will also hunt and eat the Spotted Mole on a regular basis.”
This becomes, “None of the land-based mammals active in this region, such as fox, will also hunt and eat the Spotted Mole on a regular basis.”

10) “No other animal could pose as significant a threat to the above-ground fruits as could the Spotted Mole.”
This becomes, “Some other animals could pose as significant a threat to the above-ground fruits as could the Spotted Mole.”

We hope the next time you come across an assumption question, you will not face any trouble negating the answer choices!

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Karishma, a Computer Engineer with a keen interest in alternative Mathematical approaches, has mentored students in the continents of Asia, Europe and North America. She teaches the GMAT for Veritas Prep and regularly participates in content development projects such as this blog!