Assumption Questions

An assumption is an unstated premise that supports the author’s conclusion. It’s the connection between the stated premises and the conclusion. The author’s conclusion will depend upon the assumption being valid. Assumption questions are extremely common and have stems that look like these:

  • Which of the following most accurately states a hidden assumption that the author must make in order to advance the argument above?
  • Which of the following is an assumption that, if true, would support the conclusion in the passage above?
  • Which of the following, if added to the passage, would make the conclusion logical?
  • The validity of the argument depends on which of the following?
  • Upon which of the following assumptions does the author rely?
  • The argument presupposes which one of the following?

> Free Excerpt: LSAT Logical Reasoning Guide

 

How to approach Assumption Questions

  1. Look for gaps between the premises and the conclusion. Go on an “Assumption Hunt” and spend a few seconds finding any holes in the argument.
  2. Ask yourself why the conclusion is true. Before you progress to the answer choices, try to get feel for what assumptions are necessary to fill the gaps between the premises and the conclusion.
  3. Take note of sweeping language or extreme statements.

Samples of an assumption question:

When doing assumption questions, spend maybe 10 to 20 seconds trying to think of assumptions underlying the argument.

What ideas or words are in the conclusion, but not stated in any premise or evidence? That’s an assumption.

Question #1

A study released yesterday by the American Dental Association shows that people who gargle with Berry Pop Soda are 20% less likely to get cavities. We should therefore stock up on Berry Pop Soda and prepare ourselves for increased demand.

Quick! What assumptions are in this argument? Think about it creatively and quickly. The premise is a new report coming out, and the conclusion is that it would lead to increased sales. That’s quite a leap!

Let’s quickly brainstorm some assumptions:

  1. The study was released to major media outlets and people know about it.
  2. Berry Pop soda is an attractive product that tastes good. It may be good for teeth because it tastes like toothpaste!
  3. Berry Pop is as effective as conventional mouthwashes at cavity prevention.
  4. Berry Pop has name recognition. Have you ever heard of Berry Pop?

Question #2

Apartment building owners argue that rent control should be abolished. Although they acknowledge that they would increase rents in the short term, owners argue that in the long term the rent increases would lead to greater profitability. Higher profits would lead to increased apartment construction. Increased apartment construction would then lead to a greater supply of residences and lower prices as the supply of apartments increases. Thus, abolishing rent control would ultimately reduce prices.

Express that complicated argument in your own words!

Premise 1: Abolishing rent control will increase the supply of housing (premise).

Premise 2:Greater supply leads to lower prices (premise).

Conclusion: Abolishing rent control leads to lower rents (conclusion). It is a supply/demand argument.

Try to find gaps between premises.

Look at premise 1: Abolishing rent control will increase the supply of housing.
This premise is based on the assumption that higher profits draw increased supply.

Look at premise 2: Greater supply leads to lower prices.
This is a supply/demand argument; greater supply leads to lower prices. However, there is something missing: supply and demand requires a discussion of demand. Indeed, demand is missing; that is the hidden assumption.

Question #3

Since the late 1970s and early 1980s, tax regulations and other changes have encouraged increasing numbers of venture capitalists and entrepreneurs to start new enterprises. Since 1980, some one-half million new ventures have been started. Not all have succeeded, of course.

The above statement makes which of the following assumptions?

  1. Success in starting a new business depends in large part on sound financial planning.
  2. Social incentives motivate investors just as much as financial rewards.
  3. Financial incentives are associated with new business starts.
  4. Most new business ventures succeed initially but fail later on.
  5. Venture capitalists are motivated by non-monetary gains.

This is an “after this, therefore because of this” argument. It assumes that tax changes since the 1980’s have increased the number of small businesses.

  1. May be correct, but there is nothing in the passage to substantiate it.
  2. Is the second best answer. However, it cannot be inferred that social motives are just as strong as the financial motive, given that the passage states that tax regulations motivated increasing numbers of entrepreneurs to invest.
  3. Is the correct answer.
  4. May be eliminated because of the word “most.”
  5. There is no evidence in the passage to support this answer.

Negation Test for Assumption Questions. To test if a statement is an assumption required for an argument, try to negate it. If the argument falls apart, it means that the argument requires that assumption.

In the above sample question if you got rid of the assumption that people are motivated by financial gain, then the argument falls apart. Therefore, that assumption is likely a necessary one for the argument.

> Free Excerpt: LSAT Logical Reasoning Guide

Strengthen and Weaken Questions

If unstated assumptions are the glue that holds an argument together, then weakening or strengthening the assumptions will weaken or strengthen the argument. Nearly all Strengthen/Weaken questions don’t ask you to change the conclusion or the premises, because those are fixed; it is the unstated assumptions that are in flux. The whole trick on the Strengthen/Weaken question is to strengthen or weaken the assumptions.

Strengthening and Weakening are not the same thing as proving something true or false. Instead, the right answer will support (strengthen) or cast doubt upon (weaken) the required assumptions, while also being relevant to the premises.

Here are some examples of Strengthen/Weaken question stems:

Strengthening:

  • The conclusion would be more properly drawn if it were made clear that…
  • Which of the following, if true, would most strengthen the conclusion drawn in the passage above?
  • The argument as it is presented in the passage above would be most strengthened if which of the following were true?

Weakening: (note that when it says “if true”, means that you must accept the validity of the statement)

  • Which of the following, if true, most seriously weakens the conclusion drawn above?
  • Which of the following, if true, would provide the strongest evidence against the above?
  • Which of the following, if true, casts the most serious doubt on the conclusion drawn above?

Tips for Weakening Questions:

  1. Try to find one necessary assumption in the passage. This is what the right weakening answer will often target.
  2. The All Things are Equal fallacy is very common on these questions. When things are compared over time, the assumption is that background factors remain constant (while they might be changing). A good answer might point out that some background factor did change.
  3. When you see a Weakening question that compares two things or tries to show them as similar, look for an underlying factor that makes such a comparison problematic.
  4. There will likely be two or more choices that weaken the argument. In this case, re-read the passage carefully and see which one is most directly relevant to the premises, the conclusion and assumptions.
  5. Common trap answer choices include:
    1. A statement that strengthens (and doesn’t weaken) the assumptions and the overall argument- a trick opposite.
    2. A statement with information not relevant to the argument.
    3. A statement that requires additional facts to have value.
  6. The final answer that remains is the correct answer.

Use strong language to weaken or strengthen. On most other Verbal questions, you can eliminate potential answers that use strong language. The exception is the Strengthen/Weaken questions. On these questions, sweeping words are more effective:

  • only
  • the most
  • extremely
  • all

The reason? Extreme answers will have a more powerful weakening/strengthening effect on assumptions.

Sample Questions

We’ve discussed this example several times. Use the information gained above to generate an answer based on targeting assumptions:

Question #1

The postal service is badly mismanaged. Thirty years ago, first-class letter delivery cost only three cents. Since then, the price has increased sevenfold, with an actual decrease in the speed and reliability of service.
All of the following would tend to weaken the conclusion of the argument above EXCEPT:

  1. The volume of mail handled by the postal service has increased dramatically over the last thirty years.
  2. Unprecedented increases in the cost of fuel for trucks and planes have put severe upward pressures on postal delivery costs.
  3. Private delivery services usually charge more than does the postal service for comparable delivery services.
  4. The average delivery time for a first-class letter three decades ago was slightly longer than it is today.
  5. The average level of consumer prices overall has increased fourfold over the last thirty years.

The conclusion is that the postal service is poorly managed. This is an EXCEPT stem, so we are looking for something that won’t weaken the argument.

Premise #1: the price of first-class delivery has increased sevenfold
Premise #2: there has been a decrease in speed and service.
Conclusion: The postal service is badly mismanaged
Analysis: This is the All Things are Equal fallacy. It assumes conditions don’t change, thereby making a basis of comparison over time. This compares past performance to the present day. So, of course anything that suggests that business conditions have gotten harder will excuse managerial incompetence. Anything that suggests conditions have gotten easier will not weaken the argument, so that’s what we are looking for.

Reviewing Answer Choices

The volume of mail handled by the postal service has increased dramatically over the last thirty years. This would seem to excuse the poor service/price because the service has had to overcome a massive increase in volume.

Unprecedented increases in the cost of fuel for trucks and planes have put severe upward pressures on postal delivery costs. This would seem to excuse the poor service/price because costs have increased dramatically.

Private delivery services usually charge more than does the postal service for comparable delivery services. This would seem to excuse the poor service/price because other services are not as efficient.

The average delivery time for a first-class letter three decades ago was actually slightly longer than it is today. This shows they have made improvements in service, suggesting that the postal service isn’t all that bad after all.

The average level of consumer prices overall has increased fourfold over the last thirty years.  Since the price of postage has increased seven times over, this suggests that postal prices have increased at a rate much quicker than inflation. Thus, choice 5 does support the original argument, making this the correct answer.

Question #2

In many pre-schools, children tend to commonly get colds before their resistance develops and the colds become much less frequent. It is clear that a child requires several colds before white blood cell concentrations rise high enough to effectively deal with colds.

Which of the following, if true, most seriously weakens this theory?

  1. Children commonly spread viruses and bacteria in a small closed environment.
  2. The use of Vitamin C increases resistance to the common cold and decreases its frequency.
  3. Parents stock up on cold medicine after a child gets sick that alleviate the symptoms of a cold.
  4. There are many strains of the cold virus and children develop resistance to individual strains.
  5. White blood cells fight infection and their production levels are stimulated by high infection levels.

The question is stating that the body’s immune system requires numerous infections to be properly stimulated. It is a causal argument that tries to explain an observation.

Premise #1: Children tend to get fewer colds as they progress through pre-school.
Premise #2: (unstated assumption)
Conclusion: It takes several colds to activate a child’s immune system.
Analysis: This is After This, Therefore, Because of This fallacy. It observes that as children go through pre-school the number of colds go downs. From this, the creative author develops the theory that a child’s immune system requires them to get several colds before it is fully activated.

The best way to weaken a causal argument is to suggest an alternative causal factor (find a confounding issue).

Reviewing Answer Choices

Children commonly spread viruses and bacteria in a small closed environment. Not Relevant

The use of Vitamin C increases resistance to the common cold and decreases its frequency. Not Relevant

Parents stock up on cold medicine after a child gets sick that alleviate the symptoms of a cold. This choice presents another possible reason to undermine the argument, but the medicine deals with symptoms, not the cold per se. So it is not reducing an instance of a cold, simply decreasing their symptoms (no more runny noses!).

There are many strains of the cold virus and children develop resistance to individual strains. This choice suggests an alternative explanation for the apparent improvement in a child’s ability to fight colds: the child simply becomes immune to individual viruses per se. So, the theory that a child’s immune system needs high white blood cell concentrations isn’t the case, it is an issue of exposure to certain strains. By suggesting a different causal process to explain the reduction in colds, it weakens the argument.

White blood cells fight infection and their production levels are stimulated by high infection levels. This choice supports this statement, but the question asks for what weakens it.

Trick opposites are sometimes used as junk answer choices on Strengthen/Weaken questions. If the stem asks for what weakens the passage, you’ll find a perfect answer choice for what strengthens it, and vice versa. Choice (5) in the above question about colds is an example of a trick opposite.

Inference Questions

These questions ask you to draw conclusions from the passage. While above we analyzed an argument’s assumptions, here we analyze its conclusions and implications . The conclusion of an argument in an Inference question is usually not directly stated. To find the conclusion, identify the premises and then identify what conclusion could be drawn from the premises. Inference questions differ from the other critical reasoning questions in that the argument in the passage doesn’t usually contain flaws.

  • The main point of the passage is that…
  • Which of the following statements about… is best supported by the statements above?
  • Which of the following best states the author’s conclusion in the passage above?
  • Which of the following conclusions can be most properly drawn from the data above?
  • Which of the following is [implied, must be true, implicit, most reasonably drawn] in the passage above?
  • Which of the following conclusions can most properly be drawn if the statements above are true?

How to Approach Inference Questions:

  1. Analyze scope: Inference junk answers will typically go outside the direct scope of the passage. Be careful to look directly at the scope of the question. Inference answers must be within the scope of the passage. Your opinions or information outside of the passage are always outside of the scope.
  2. Don’t jump into the Assumption Hunt. These questions usually don’t carry much in the way of glaring assumptions. Instead, these questions generally test your ability to derive a conclusion from stated premises.
  3. Knock out answers with extreme wording. Inference answers typically do not use only, always, never, best or any strong words that leave little wiggle room. The right answers on Inference questions will generally use more qualifiers and less extreme language.
  4. Try to fully understand what the passage’s point is and the exact reasoning so that if the question asks you to extend that reasoning, you are able to accurately do so.
  5. Use the process of elimination. Inference questions typically have two or three good answers that are semi-plausible. The best way to tackle these questions is to gradually eliminate the possible answers until you have one or two and then choose the last one by scope.

Sample Questions

Although Locke has been hailed as a giant figure in European intellectual history, his ideas were largely borrowed from his predecessors, who are now unfairly neglected by historians. Furthermore, Locke never wrote a truly great book; his most widely known works are muddy in style, awkwardly constructed, and often self-contradictory.

With which of the following would the author most likely agree?

  1. Locke made use of ideas without acknowledging his predecessors as the sources of those ideas.
  2. Current historians are re-evaluating the work of Locke in the light of present-day knowledge.
  3. Locke’s contributions to the development of European thought have been greatly exaggerated.
  4. Historians should reexamine Locke’s place in European intellectual history.
  5. Although Locke’s ideas were important, his way of expressing them in writing was sadly inadequate.

The author makes two assertions about Locke: that his ideas were not original and that his books were not very good. On the basis of these assertions, the author concludes that Locke’s reputation as an intellectual giant is undeserved. Choice (3) accurately summarizes this conclusion.

  1. Focuses on a subsidiary point, not the main idea; moreover, it makes an assumption unsupported by the passage namely, that Locke did not acknowledge the sources of his ideas.
  2. Is wrong because although the passage clearly indicates that the author is “re-evaluating” Locke’s work, it does not suggest that “current historians” in general are doing so.
  3. This choice best expresses the point, that Locke’s contributions were not original.
  4. Is tricky because it is a good answer, but it is not the best answer. (4) implies that the author recommends that other historians re-examine Locke. Since no recommendation exists in the argument, Choice (3) is the only option.
  5. Not addressed.

In 2008, Gotsland used three-times as much energy from non-renewable sources as renewable sources. Gotsland’s proposed ten-year energy plan would result in the country using as much renewable as non-renewable energy by 2018, while using a larger amount of energy than in 2008.

Which of the following must happen for Gotsland’s plan to work?

  1. By 2018, Gotsland will more than triple its use of energy sources.
  2. Gotsland will have to make a political effort to have a more sustainable energy economy.
  3. By 2018, Gotsland will have to decrease its reliance on non-renewable energy sources.
  4. By 2018, Gotsland will more than triple its use of renewable energy sources over 2008 levels.
  5. New technologies must be developed to make the cost of renewable resources more competitive with renewables.

In questions like these where they start throwing around numbers and you scratch your head…”didn’t I already do the quant section?”. It might help to use a little Plug In.

In a quant math problem we would translate words to numbers, so let’s do that here. In 2008, Gotsland used three-times as much energy from non-renewable sources as renewable sources. Well, we can substitute 50 megawatts of renewable energy and 150 megawatts of non-renewable for what we have in 2008 (total of 200 megawatts).

Looking at the next statement, Gotsland’s proposed ten-year energy plan would result in the country using as much renewable as non-renewable energy by 2018, while using a larger amount of energy than in 2008. Well, this means that in 2018 they will be using more than 200 megawatts AND renewables will be at least 150 (what the current non-renewables are). So it needs to triple its use of renewables.

Now that we have our facts laid out we can review the answer choices.

  1. Gotsland does not need to triple its energy sources (just renewables).
  2. Isn’t relevant.
  3. Gotsland doesn’t need to decrease its use of non-renewables. It is mathematically possible for it to increase the total usage of total energy. In this scenario, non-renewables remains at 150 and renewables increases to 150 as well.
  4. Yes, Gotsland MUST at least triple its use of non-renewables (to be at least 150 megawatts).
  5. This may be the case, but there is nothing in the question to make this point.

Why is there a math question in my Verbal section? Some inference questions (like the above) use basic number line analysis or proportions. This is just testing your ability to use numbers in the context of critical reasoning.

> Free Excerpt: LSAT Logical Reasoning Guide

Flaw Questions (Uncommon)

These questions ask you to recognize what’s wrong with an argument. Most of these questions require you to point out a fallacy in the argument. These should be easy because we have an extensive section above covering the most common logical flaws.

Here are typical flaw questions:

  • Which one of the following contains a flaw that most closely parallels the flaw contained in the passage?
  • Which one of the following best identifies the flaw in the above argument?
  • In presenting her position, the author does which one of the following?

Question #1

John: We should oppose any attempt to register firearms. Such regulation is the first step to confiscation of all weapons and the elimination of our constitutional right to bear arms.

Ted: This is preposterous. Many things in society are registered, such as cars, babies, boats and lanes, yet these items have never been confiscated.

What are the flaws in the reasoning above?

Analysis: Ted is making a faulty analogy between registration of guns and registration of cars and babies. But, guns are frequently used as instruments of intentional violence and therefore may be more likely targets for confiscation.

John is making a slippery slope argument that registration of firearms must invariably lead to the elimination of a constitutional right

Question #2

John: I don’t want to die in an accident. Every few days on the TV news I hear of a major plane crash somewhere in the world. I would never fly in planes, they are too dangerous.

Ted: Nonsense, statistics show that airplanes are the safest mode of transportation on a per-mile basis.

John: The answer then is not to travel such long distances.

Analysis: John is pointing out that plane crashes are always in the news, therefore they must be very dangerous. The TV news, however, is a biased sample of all accidents. Minor traffic fatalities around the world rarely make the news, but plane crashes do.

Ted points out the obvious that on a per-mile basis, planes are safer, yet planes can travel ten thousand miles, so a long trip does entail risk. John’s final analysis is to play it safe and not to travel long distances at all.

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Prep Guide

Table of Contents
Ch. 1: Introduction
Ch. 2: Reading Comprehension
Ch. 3: Logic Reasoning
Critical Reasoning
Argument Structure
Reasoning Skills
Common Questions
Advanced Questions
Sample Questions
Ch. 4: Logic Games
Ch. 5: Sample Test

Read a free excerpt of the PowerScore LSAT Logical Reasoning Bible™, the most comprehensive book available for the Logic Reasoning section of the LSAT. This book will provide you with an advanced system for attacking any Logical Reasoning question that you may encounter on the LSAT.