Lesson 14 of 46 · Reading Comprehension
Strengthen, weaken and explain
Use the gap in an argument to find what strengthens or weakens it, and resolve an apparent paradox with the fact that lets both sides be true.
About 20 minutes
In this lesson
- Find the choice that most weakens or strengthens an argument by aiming at its gap.
- Resolve an apparent discrepancy with a fact that makes both observations true together.
- Reject choices that are irrelevant, merely restate the evidence or push the wrong way.
The idea
Questions that add new information
Strengthen, weaken and explain questions are unusual in one respect: the right answer brings in information that is not in the passage. You accept each choice as true and ask what it does to the argument. This is the reverse of detail and inference questions, where anything not in the passage is out. Mixing up the two habits is the main source of errors here.
Start from the gap
Before reading the choices, do what the previous lesson taught: find the conclusion, the evidence, and the gap between them. Almost every right answer is aimed at that gap.
- To weaken, a choice shows the gap is real: it gives an alternative cause, shows the sample is skewed, or shows that conditions changed.
- To strengthen, a choice closes the gap: it rules out an alternative cause, shows the sample is typical, or supplies the missing link.
A weakener does not have to prove the conclusion false. It only has to make it less likely. Likewise, a strengthener does not have to prove the conclusion; it makes it more likely.
The same argument, both ways
Take: "Since a café chain introduced a discount for customers who bring reusable cups, the share of its drinks sold in disposable cups has fallen from 90% to 70%. The chain's report credits the discount." The gap is sequence to cause: the fall followed the discount, but was it caused by it?
| Choice | Effect |
|---|---|
| Over the same period, the city introduced a charge on all disposable cups. | weakens: an alternative cause |
| In the chain's branches outside the city, where no such charge applies, the share fell by a similar amount after the discount began. | strengthens: rules that alternative out |
| Many customers say they like the discount. | little effect: liking it does not show it changed behaviour |
| Reusable cups are better for the environment. | irrelevant: says nothing about the cause of the fall |
Explain questions: let both facts be true
Some questions describe two facts that seem to clash and ask which choice "helps to explain", "resolves" or "reconciles" them. For example: a town installed brighter street lights, and reported burglaries then rose.
The right answer does not deny either fact. It adds something that makes both expected. Here: with brighter lighting, more burglaries are seen by neighbours and passers-by, and so more are reported, even if no more take place. Now brighter lights and a rise in reported burglaries fit together.
To find it, state the tension exactly ("we would expect X, but we see Y") and look for a choice that makes Y what we should have expected. Choices that explain only one of the two facts, or that make the tension worse, are wrong.
Wrong choices you will meet
- Irrelevant: true, on topic, but not touching the gap.
- Restates the evidence: repeats what the argument already says; adds no support.
- Wrong direction: a strengthener among weakener choices, or the reverse. Read the question word again before choosing.
- Off target: a choice that would be decisive if true but is about a different situation from the argument's.
- Explains half: in explain questions, accounts for one fact only.
A routine
- Read the question first, so you know whether you are strengthening, weakening or explaining.
- Find the conclusion and the gap, or state the tension in one sentence.
- Predict the kind of fact that would work (an alternative cause, a comparison group, a reporting effect).
- Treat each choice as true and ask what it does to the gap. Pick the one with the largest effect in the asked direction.
Worked examples
Example 1: Weakening a causal claim
Since a café chain introduced a discount for customers who bring reusable cups, the share of its drinks sold in disposable cups in its city branches has fallen from 90% to 70%. The chain's report concludes that the discount caused the fall.
Which of these, if true, most weakens the report's conclusion?
- Customers who use the discount visit the café more often than before.
- During the same period, the city began charging customers for every disposable cup they take.
- The discount is the largest the chain has ever offered.
Conclusion: the discount caused the fall. Evidence: the fall came after the discount. Gap: sequence to cause, so look for another cause that arrived at the same time.
Choice 1 is about customers who already use the discount; it does not question whether the discount caused the change. If anything it fits the report.
Choice 2 gives a different cause, arriving in the same period and pushing customers away from disposable cups. If it is true, the fall may owe little to the discount.
Choice 3 says the discount was large, which makes the report's story slightly more plausible, not less.
Answer
The city's charge on disposable cups most weakens the conclusion: it is an alternative cause that coincides with the discount. The tempting wrong answer is the size of the discount, which sounds relevant but pushes in the report's favour.
Example 2: Explaining an apparent paradox
After a town installed brighter street lights in its residential areas, the number of burglaries reported to the police in those areas rose. Which of these would most help to explain the rise?
- The new lights use less electricity than the old ones.
- Burglaries in the town's commercial areas fell over the same period.
- With brighter lighting, more burglaries are noticed by neighbours and passers-by, and more of those noticed are reported.
State the tension: brighter lights are expected to deter burglary, yet reported burglaries rose.
Predict: something that makes a rise in reports expected even if burglaries did not rise, or a reason burglaries might rise.
Choice 1 is about electricity; it touches neither fact. Choice 2 is about different areas; it leaves the residential rise unexplained.
Choice 3 makes more burglaries visible and so more reported. Both facts are now expected: the lights work as designed, and reports rise.
Answer
The third choice explains the rise: brighter lighting increases the share of burglaries that are noticed and reported. The trap is the commercial-area choice, which is about burglary and lighting's effects but explains a different place.
Common traps
Rejecting a choice because it is not in the passage
In these questions the answer is new information by design. A reader trained to reject anything not stated will reject the right answer. Accept each choice as true and judge what it does.
Answering the opposite question
In a weaken question, a strong strengthener is very tempting, because it clearly bears on the argument. Re-read the question word before you choose, and check the direction of your choice's effect.
Explaining only half the paradox
A choice that explains why burglaries might rise, but contradicts the lights being brighter, or explains one fact while ignoring the other, does not resolve the tension. The right choice leaves both facts standing and makes them fit.
Choices that only say people like something
"Customers say they like the discount" or "staff prefer the new lamps" rarely strengthens a causal claim. Preferences are not behaviour. Look for choices that bear on what actually happened.
Check yourself
Answer each question before you open its answer.
Question 1: Weaken
Reading Comprehension: argument
A company replaced its office lighting with lamps designed to imitate daylight. In the six months after the change, staff took 20% fewer sick days than in the six months before it. The facilities manager concludes that the new lighting improved the staff's health.
Which of the following, if true, most seriously weakens the manager's conclusion?
- A.Most staff said in a survey that they prefer the new lamps.
- B.The new lamps use less electricity than the old ones.
- C.The six months before the change were the region's winter months, when illness is most common, and the six months after were spring and summer.
- D.Several other companies that installed similar lamps also reported fewer sick days afterwards.
- E.A few staff members found the new light too bright.
Show the answer
Answer: C. The six months before the change were the region's winter months, when illness is most common, and the six months after were spring and summer.
Working
The gap is sequence to cause: sick days fell after the change. The seasonal choice offers an alternative cause that fits the timing exactly: the "before" period was the high-illness season and the "after" period was not. With that true, a fall in sick days was to be expected without any effect from the lamps.
Why the other options are wrong
- A. A preference says nothing about health or sick days; it neither supports nor undermines the causal claim.
- B. Electricity use is irrelevant to whether the lighting changed sick days.
- D. This supports the manager's conclusion by repeating the pattern elsewhere; it strengthens rather than weakens.
- E. Discomfort for a few people does not bear on the overall fall in sick days.
What carries over
When a before-and-after comparison is the evidence, look for anything else that differed between the two periods.
Question 2: Strengthen
Reading Comprehension: argument
Researchers found that people who own dogs walk more each week, on average, than people who do not. They concluded that owning a dog causes people to walk more.
Which of the following, if true, most strengthens the researchers' conclusion?
- A.The dog owners in the study were, on average, younger than the people without dogs.
- B.Some dog owners walk their dogs for only a few minutes a day.
- C.People who enjoy walking are more likely than others to decide to get a dog.
- D.Dog owners in cities walk less, on average, than dog owners in the countryside.
- E.In a group followed over several years, people's weekly walking rose after they acquired a dog, compared with similar people who did not acquire one.
Show the answer
Answer: E. In a group followed over several years, people's weekly walking rose after they acquired a dog, compared with similar people who did not acquire one.
Working
The evidence is a correlation; the gap is that walkers might get dogs, or that some third factor drives both. Following the same people before and after they acquire a dog, against a similar group that does not, shows walking rising after the dog arrives. That closes both the reverse-causation and the third-factor gaps, so it makes the causal conclusion more likely.
Why the other options are wrong
- A. Age is an alternative explanation for walking more, so this weakens the conclusion.
- B. This concerns a few owners and says nothing about whether owning a dog changes how much people walk.
- C. This suggests the causation runs the other way, from walking to dog ownership, and so weakens the conclusion.
- D. A difference among dog owners does not address whether owning a dog causes more walking.
What carries over
A causal claim from a correlation is best strengthened by evidence that the effect follows the cause in the same people, against a comparison group.
Question 3: Explain
Reading Comprehension: argument
In the district of Morrow, the number of bicycle thefts reported to the police doubled in the year after the police launched an online form that lets residents report a theft in two minutes. Over the same year, insurers in the district received about the same number of claims for stolen bicycles as in the year before.
Which of the following, if true, most helps to explain the difference between the two trends?
- A.The police increased their patrols in the district during the year.
- B.Sales of new bicycles in the district rose slightly during the year.
- C.Many residents did not learn of the online form until late in the year.
- D.Most thefts that had gone unreported before the form existed involved bicycles too cheap for their owners to have insured.
- E.Thieves in the district mostly target expensive bicycles.
Show the answer
Answer: D. Most thefts that had gone unreported before the form existed involved bicycles too cheap for their owners to have insured.
Working
State the tension: reports doubled, but insured losses did not change. If the easy form mainly brought in reports of thefts that previously went unreported, and those were mostly uninsured cheap bicycles, then reports would rise while claims stayed level, with no real rise in theft needed. Both facts are then expected.
Why the other options are wrong
- A. More patrols might reduce thefts, but that explains neither the doubling of reports nor why claims did not change.
- B. More bicycles could mean more thefts, but then insurance claims would be expected to rise too, so the gap remains.
- C. This would limit the rise in reports; it does not explain why reports and claims moved differently.
- E. Expensive bicycles are the ones likely to be insured, so a real doubling of their theft would raise claims; this deepens the puzzle.
What carries over
When two measures of the same thing move apart, look for a choice showing they count different cases.
Key points
In strengthen, weaken and explain questions, treat every choice as true; the answer is new information.
Aim at the gap: weakeners widen it, strengtheners close it.
An explanation leaves both facts standing and makes them fit together.
Re-read the question word before choosing, to avoid answering its opposite.
All questions here are original and written for UniExamer; none comes from the test maker.
Written by the UniExamer team with AI assistance. Every worked example and check question was re-solved by an independent checker before publication. No subject expert has reviewed this lesson yet. If you find a mistake, write to support@uniexamer.com.