Assumption Questions

Assumptions, which were defined on the second page of this section, appear frequently in LR. Assumption questions ask you to identify the Sufficient or Necessary Assumption made in the stimulus.

Necessary Assumption questions have stems phrased in the following ways:

  • The argument requires/depends on/relies on the assumption that
  • Which of the following is an assumption on which the argument relies/depends?
  • Which one of the following is an assumption the argument requires?
  • The argument requires/depends on/relies on assuming which one of the following?

Sufficient Assumption questions are phrased like this:

  • The conclusion follows logically if which one of the following is assumed?
  • The conclusion of the argument can be properly drawn if which one of the following is assumed?

Notice that Necessary Assumption questions always contain a word that means “necessary” or “required,” while Sufficient Assumption questions ask for a guarantee that the conclusion will be reached.

Sample Assumption Questions

Example #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 made 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. People know about the study released yesterday.
  2. People believe in the credibility of the study whose results were published yesterday.
  3. The taste of Berry Pop soda is acceptable to people.
  4. There aren’t lots of other sodas available that are more effective at preventing cavities than Berry Pop Soda.
  5. There isn’t a cavity prevention method that is a suitable and/or favorable alternative to gargling with soda.

These predictions will help you wade through the answer choices without getting confused or wasting time!

Example #2

Apartment building owners argue that rent control should be abolished. Although they acknowledge that this will increase rent prices in the short term, owners argue that in the long term the greater profitability will lead to an increase in the construction of new apartment buildings. Increased apartment construction will then lead to a greater supply of residences and, ultimately, lower rent prices as the increasing supply decreases demand. Thus, abolishing rent control will rapidly 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 quickly leads to lower rent.

Try to find gaps between the premises and the conclusion.

This is a supply/demand argument; increasing profitability leads to a greater supply which in turn leads to lower prices. However, the link between the chain of evidence and the conclusion is shaky. The property owners’ argument has a lot of “ifs” to begin with and, though we need to accept the evidence chain as factual (premises are always accepted as true), we have to keep in mind that it is worded as an eventual reality, not an immediate outcome. The conclusion, therefore, assumes that the outcome is guaranteed, firstly, and, more importantly, going to happen rapidly.

Question #1: Necessary Assumption

If lawmakers are to enact legislation that benefits citizens, they have to consider the actual consequences of enacting any proposed law. Modern lawmakers fail in enacting laws that are beneficial to citizens. Because they are focused on advancing their own careers, lawmakers present legislation incisively, which causes their colleagues to react with total disdain or unbridled enthusiasm for the legislation.

The argument relies on which one of the following assumptions?

A) Unless lawmakers become less preoccupied with their own careers, legislation will not benefit constituents.

B) Legislative bodies that enact beneficial laws are successful legislatures.

C) Unless citizens adhere to laws, the passage of these laws cannot be beneficial.

D) Lawmakers considering a proposed law about which they are disdainful or enthusiastic do not consider the actual consequences of that law.

E) The strong feelings of lawmakers about a proposed legislation cause their inability to consider the actual consequences of that legislation.

Denial Test for Necessary Assumption Questions

To test whether a statement is an assumption required for an argument, try to negate it. Plug the negated assumption back into the argument. 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, then the argument falls apart. Therefore, the assumption is necessary for the argument to work.

Think how the Denial Test applies to this question.

Question #2: Sufficient Assumption

Although the geologic record sometimes implies that meteors hitting the earth have sometimes preceded mass extinctions, there have been many extinctions that did not come after a collision with a meteor. Similarly, there are many meteoric collisions that don’t precede a mass extinction. Thus, the geologic record provides evidence that there is no causal link between meteors and mass extinctions on a consistent basis.

Which one of the following, if true, allows the argument’s conclusion to be properly drawn?

A) All meteoric collisions would be followed by extinctions if there were a consistent causal link between meteoric collisions and extinctions.

B) Unless mass extinctions have consistently followed meteors hitting the earth, meteoric collision and mass extinction cannot be causally linked.

C) Very few, if any, of the mass extinctions that occurred after a meteoric collision followed a meteoric collision about which the geologic record did not imply.

D) If there is no consistent causal link between collisions and extinctions, not all meteoric collisions could have been followed by a mass extinction.

E) Even if not every meteoric collision has been followed by a mass extinction, there could be a consistent causal link between meteors and extinctions.

Strengthen and Weaken Questions

Strengthen and Weaken questions ask you to find statements that increase (strengthen) or decrease (weaken) your belief in the argument. Since the premises are taken to be true, the way to increase or decrease the belief in an argument is to increase or decrease belief in the assumptions of the argument.

Please remember that a strengthen correct option choice will not make the argument fool-proof; it’ll just make the argument stronger. Similarly, a weaken correct choice will not demolish the argument completely; it’ll just make it weaker to some extent.

Here are some examples of Strengthen/Weaken question stems:

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

  • 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?

Weaken:

  • 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 Weaken Questions:

  1. Try to find one necessary assumption in the passage. This is what the right weaken 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 — when in reality they might have changed. A good answer might point out that some background factor did change.
  3. When you see a Weaken 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 the assumptions.
  5. Common trap answer choices include:
    • A statement that strengthens (and doesn’t weaken) the assumptions and the overall argument — a trick. This is the opposite of what you want.
    • A statement with information not relevant to the argument.
    • 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 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 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 higher than inflation. Thus, choice 5 supports the original argument, making this the correct answer.

Question #2

In many pre-schools, children commonly tend to 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 that alleviates the symptoms of a cold after a child gets sick.
  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 goes 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.

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 that alleviates the symptoms of a cold after a child gets sick. 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 but simply decreasing its 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. 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 present you a series of facts and ask you to find a statement that is most supported by the facts. In other words, you need to find a statement that is most likely to be true if the given statements in the stimulus are true. Here are a few examples of Inference question stems:

  • 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. Read and Understand the Passage: Be very precise in what each sentence means and what it doesn’t mean. Also, try to see how the sentences are inter-related.
  2. Predict a possible Inference: Before looking at the option statements, try to think of possible statements that you can infer from the passage. Doing so will significantly increase your understanding of the passage.
  3. Evaluate Option Statements: Read and understand the option statements. Eliminate four option statements for solid reasons and accept one that you think is correct.

Sample Questions

Question #1

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. The focus is on a subsidiary point, not the main idea; moreover, it makes an assumption unsupported by the passage: that Locke did not acknowledge the sources of his ideas.
  2. It 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. The option 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.

 

Question #2

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 more sustainable energy.
  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 increase 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. 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 fact 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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