Unit 5

Weakening Arguments

About this unit

Read an argument and find the statement that most seriously undermines, contradicts, or exposes a flaw in its reasoning. You will learn to spot the hidden assumptions every argument makes — and find what would prove those assumptions wrong.

What types of questions will you face?

1A statistic or comparison is used to draw a conclusion — find what shows the comparison is unfair
2A cause-and-effect claim is made — identify the evidence that shows correlation, not causation
3A proposal or recommendation is given — find what would make it ineffective or counterproductive
4A generalisation is drawn — find the counterexample or hidden factor that undermines it
5A "success story" argument is made — identify what alternative explanation weakens the conclusion

Skills you will build

Identifying the hidden assumption that an argument depends on
Recognising when a sample is too small or unrepresentative
Spotting alternative explanations for an observed outcome
Understanding how context (e.g. population size) can make a statistic misleading
Evaluating the relevance of each answer option to the specific argument made

By the end of this unit, you will be able to

Identify the weakest point in any argument quickly and reliably
Spot when a conclusion goes beyond what the evidence actually supports
Recognise the classic logical pitfalls: cherry-picked data, false comparisons, unsupported generalisations
Apply critical thinking to arguments across health, science, policy, and everyday life

Difficulty profile

Medium difficulty (avg 3.17). These questions are harder than Strengthening Arguments because you need to understand the argument deeply enough to find what would break it. Some involve subtle statistical traps.

Exam tip: Weakening Arguments

Ask: "What does this argument ASSUME to be true?" Then find the answer that shows that assumption is false or unreliable. The weakening answer doesn't have to disprove the conclusion — it just needs to cast serious doubt.

Sample Questions

Lesson 1 of 2Weakening ArgumentsIntermediate

Weakening Arguments questions test one specific mental habit: reading an argument, identifying what it assumes to be true, and then finding the evidence that shows that assumption does not hold.

This format appears consistently across every OC Thinking Skills test. The ability to quickly isolate the hidden assumption separates students who guess from students who score reliably on Evaluating Arguments.

The examiner wants to confirm that you can identify the single claim an argument is trying to prove and then select the statement that most directly undermines it — not something vaguely contrary or emotionally opposite, but something that logically breaks the argument.

An argument makes a general claim about why something happens — typically a one-cause explanation. Three of the four options restate the claim, mildly support it, or are irrelevant. The correct weakener provides a different explanation for the same behaviour or outcome.

Best approach: Ask: "What does this argument ASSUME must be true?" Then ask: "Which option shows that assumption is false or incomplete?" The answer that offers the most direct and powerful counter-explanation wins — a rival cause, an overlooked exception, or a fact that reverses the conclusion.

Question

People do not eat certain foods because they are picky eaters. This is especially demonstrated in our present world, due to the large variety of foods that can now be found in a large selection of stores, cafes and restaurants.

Which of the following best weakens the argument?

A $People do not eat certain foods because they do not wish to.$
B $People eat whatever they want because they want to.$
C $People do not consume food at all.$
D $People do not eat certain foods due to allergies that can harm them.$

Decided on your answer? Check how you went below.

Correct Answer

People do not eat certain foods due to allergies that can harm them.

Step-by-Step Explanation

What does the argument assume? The argument says that people avoid certain foods solely because they are picky eaters — it's purely a matter of personal taste and preference. To weaken this, we need an option that shows there is a different, equally valid reason why people avoid certain foods that has nothing to do with being fussy. Check each option: Option What it says Effect on the argument A People avoid food because they don't want to Just restates the argument in different words — picky eating IS choosing not to eat something ✗ B People eat freely Vague and doesn't explain why some foods are avoided ✗ C People don't consume food at all Clearly false and irrelevant ✗ D People avoid foods due to allergies that can harm them Provides a completely different reason — medical necessity, not preference ✓ Why D wins: Someone with a life-threatening peanut allergy is not being "picky" — they are protecting their health. If this is true, the argument's claim that all food avoidance is due to pickiness is wrong. There is at least one serious alternative reason that has nothing to do with personal taste. The answer is D.

Lesson 2 of 2Weakening ArgumentsIntermediate

Now for a more subtle and demanding type of weakening question — one that exposes a hidden statistical flaw rather than simply offering an alternative cause. These questions test whether you think critically about numbers, not just accept them at face value.

Statistical fallacy questions appear regularly in the harder half of OC TS Evaluating Arguments items. The "base rate" trap is one of the most frequently tested logical errors in the entire exam series.

The examiner is testing whether you can spot the missing denominator — the "base rate" — that makes a raw count statistic meaningless without context. More accidents in one place does not automatically mean higher individual risk; it may simply mean more people go there.

An authority compares the number of events (accidents, crimes, illnesses) at two different locations and concludes that one location is more dangerous. The correct weakener reveals that far more people use the supposedly "dangerous" location — so the risk per person is actually lower there.

Best approach: Whenever an argument says "more X happens at Place A, therefore Place A is riskier", immediately ask: "Do more people go to Place A?" The answer that reveals a much larger user base transforms the raw count into a rate — and that rate may tell a completely different story.

Question

A local council report found that significantly more bicycle accidents happen on the 'Blue Coastal Path' than on the 'Mountain Forest Trail.' Based on this data, the Head of Safety argued: "The Blue Coastal Path is a much more dangerous track for individual cyclists, and anyone riding there is at a higher risk of having an accident than if they rode the Mountain Forest Trail."

Which one of these statements, if true, most weakens the Head of Safety's argument?

A $The Mountain Forest Trail has more steep hills and sharp turns than the Blue Coastal Path.$
B $Most people who ride on the Mountain Forest Trail are experienced professional cyclists.$
C $The Blue Coastal Path is five times longer than the Mountain Forest Trail.$
D $Ten times as many cyclists use the Blue Coastal Path every day compared to the Mountain Forest Trail.$

Decided on your answer? Check how you went below.

Correct Answer

Ten times as many cyclists use the Blue Coastal Path every day compared to the Mountain Forest Trail.

Step-by-Step Explanation

What is the Head of Safety's argument? Blue Coastal Path has more accidents \to therefore it is more dangerous for each individual cyclist. The hidden flaw: total count vs. individual risk Risk per person = Accidents \div Total cyclists. The Head of Safety only looked at the top number (accidents) and ignored the bottom number (how many people actually ride each path). A simple illustration: Path Accidents Cyclists Risk per person Blue Coastal 100 10,000 1 in 100 (1%) Mountain Forest 1050 1 in 5 (20%) Even though the Coastal Path had more total accidents, each individual cyclist there was far safer. Check each option: Option What it says Effect on the argument A Mountain trail has steep hills and sharp turns Makes the mountain trail sound dangerous — but doesn't explain the accident count difference ✗ B Mountain trail riders are experienced professionals Explains why fewer accidents there, but doesn't give the denominator (how many people ride it) ✗ C Coastal path is five times longer More length could mean more accidents, but doesn't directly give us the per-person risk ✗ D 10\times more cyclists use the Coastal Path daily Directly provides the missing denominator — the accident rate per person on the Coastal Path is far lower ✓ Why D is the strongest weakener: If 10 times more people use the Coastal Path, we would expect roughly 10 times more accidents even if both paths were equally safe. Option D shows the Head of Safety compared raw totals without accounting for usage — the individual risk calculation completely changes. The answer is D.

Up next: Unit 6

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Option	What it says	Effect on the argument
A	People avoid food because they don't want to	Just restates the argument in different words — picky eating IS choosing not to eat something ✗
B	People eat freely	Vague and doesn't explain why some foods are avoided ✗
C	People don't consume food at all	Clearly false and irrelevant ✗
D	People avoid foods due to allergies that can harm them	Provides a completely different reason — medical necessity, not preference ✓

Path	Accidents	Cyclists	Risk per person
Blue Coastal	100	10,000	1 in 100 (1%)
Mountain Forest	10	50	1 in 5 (20%)

Option	What it says	Effect on the argument
A	Mountain trail has steep hills and sharp turns	Makes the mountain trail sound dangerous — but doesn't explain the accident count difference ✗
B	Mountain trail riders are experienced professionals	Explains why fewer accidents there, but doesn't give the denominator (how many people ride it) ✗
C	Coastal path is five times longer	More length could mean more accidents, but doesn't directly give us the per-person risk ✗
D	10× more cyclists use the Coastal Path daily	Directly provides the missing denominator — the accident rate per person on the Coastal Path is far lower ✓