In this guide
"Which of the following, if true, would most weaken the author's argument?" You will meet some version of this question in CAT. It may sit under an RC passage, or it may hide inside a para summary where you must see which sentence is the conclusion. Either way, the skill is the same: seeing how an argument is put together and where it is weak.
This guide breaks arguments into parts, gives you one test that settles most assumption questions, lists the flaws examiners use again and again, and works through original arguments with every option explained.
Where critical reasoning appears in CAT
In recent CAT papers, argument questions have appeared mostly within RC sets rather than as a separate block of short arguments. Typical stems ask what the author assumes, what would strengthen or weaken the argument, or what the author would most likely agree with. Para summary and para completion also depend on telling a conclusion from its support.
The parts of an argument
- Premise: a reason or piece of evidence offered.
- Conclusion: what the author wants you to accept because of the premises.
- Assumption: an unstated link that must hold for the premises to support the conclusion.
Signal words help you label sentences quickly.
| Role | Signal words |
|---|---|
| Conclusion | therefore, so, thus, hence, it follows that, this shows that |
| Premise | because, since, given that, as shown by, for |
| Counterpoint | although, admittedly, while it is true that |
| The author's turn | but, yet, however, the real issue is |
Not every argument uses signal words. When it doesn't, ask of each sentence: "Is this being argued for, or used to argue?"
The question types
| Question | What you are looking for |
|---|---|
| Assumption | The missing link without which the argument fails |
| Strengthen | New information that closes a gap or rules out an alternative |
| Weaken | New information that opens a gap or offers an alternative explanation |
| Inference | What must follow from the statements given (see inference questions) |
| Flaw | The error in the reasoning, described in general terms |
| Explain a paradox | A fact that lets two apparently conflicting statements both be true |
The negation test for assumptions
To check whether an option is a necessary assumption, negate it, then ask whether the argument still stands.
- If the argument collapses when the option is negated, the option is an assumption.
- If the argument survives, the option may be relevant, but it is not required.
This test is powerful because it filters out options that are merely helpful or merely true.
The flaws that recur
| Flaw | What happens | What weakens it |
|---|---|---|
| Correlation taken as cause | Two things happen together, so one must cause the other | Another factor that changed at the same time |
| Unrepresentative sample | A small or unusual group stands in for everyone | Evidence that the group differs from the whole |
| Ignoring other explanations | Only one cause is considered | A plausible rival cause |
| False analogy | What held in one case is assumed to hold in a different one | A relevant difference between the cases |
| Necessary taken as sufficient | Something needed is treated as enough | A case where it was present but the result did not follow |
Most CAT weaken questions attack the first or third flaw. Look for what else changed.
Worked example 1: weaken
After a company introduced flexible working hours, its annual staff survey showed satisfaction rising from 58% to 71%. Flexible hours, therefore, improve employee satisfaction.
Which of the following, if true, most weakens the argument?
(a) Some employees did not use the flexible hours option.
(b) In the same year, the company raised salaries in every department by 15%.
(c) Satisfaction at rival firms is below 71%.
(d) Flexible hours are common in many industries.
Answer: (b). It offers a rival cause that changed at the same time, so the rise in satisfaction may have nothing to do with flexible hours.
- (a) barely matters. A policy can raise average satisfaction even if some people don't use it.
- (c) compares with other firms, which says nothing about why this company's figure rose.
- (d) is irrelevant to cause and effect here.
Worked example 2: assumption
The city's new cycle lanes have been used by thousands of riders a day since they opened. The lanes have therefore reduced car traffic in the city centre.
The argument assumes that:
(a) cycling is healthier than driving.
(b) every resident of the city owns a bicycle.
(c) many of the riders would otherwise have made those trips by car.
(d) the lanes were built within their budget.
Answer: (c). Negate it: "few of the riders would otherwise have driven". Perhaps they would have walked or taken the bus. Then heavy use of the lanes says nothing about car traffic, and the argument collapses.
- (a) may be true but is irrelevant to traffic.
- (b) is far stronger than the argument needs. Negate it ("not every resident owns a bicycle") and the argument is untouched.
- (d) concerns cost, not traffic.
Worked example 3: strengthen
Students at schools that begin at 9 a.m. score higher in morning tests than students at schools that begin at 7.30 a.m. Later start times, therefore, improve students' performance.
Which of the following, if true, most strengthens the argument?
(a) Schools that begin at 9 a.m. are mostly in wealthier districts.
(b) Many teachers prefer later start times.
(c) Morning tests are harder than afternoon tests.
(d) When one school moved its start from 7.30 to 9 a.m., its students' scores rose while its teachers, syllabus and intake stayed the same.
Answer: (d). It isolates the start time: the same school, the same people, and only the timing changed.
- (a) weakens the argument, because wealth could explain the higher scores.
- (b) concerns teachers' preferences, not student performance.
- (c) applies equally to both groups, since both took morning tests.
Practice set
- "A town installed brighter street lights on its main road, and reported thefts on that road fell by a third the following year. The council concludes that brighter lighting deters theft." Which most weakens the conclusion?
- (a) In the same year, reported thefts fell by a similar proportion on streets where the lighting was not changed.
- (b) The new lights use less electricity than the old ones.
- (c) Some residents complained that the new lights were too bright.
- (d) Thefts on the main road had been rising for several years before the change.
- "Online courses let students replay lectures as often as they like. Therefore, students in online courses will understand the material better than those who attend lectures in person." The argument assumes that:
- (a) online courses are cheaper than courses taught in person.
- (b) lectures given in person are always dull.
- (c) students in online courses will actually replay lectures where they find the material difficult.
- (d) every student prefers online learning.
- "After a hospital introduced a more sensitive screening test for a disease, the number of recorded cases in the district rose sharply. Yet doctors believe that the actual spread of the disease did not change." Which best explains this?
- (a) The disease is more common among older people.
- (b) The new test detects mild cases that the old test missed.
- (c) The hospital hired more staff that year.
- (d) The old test was cheaper than the new one.
Answers:
- (a). If thefts fell just as much where nothing changed, something other than the lighting probably caused the fall. (b) and (c) are irrelevant to theft. (d) strengthens the council's case, because the trend reversed after the lights went in.
- (c). Negate it: if online students don't replay the lectures, the stated advantage does nothing, and the conclusion fails. (a) is irrelevant. (b) and (d) are extreme and not needed.
- (b). More cases are recorded because more are detected, even though no more people are ill. (a) explains who gets the disease, not the rise in records. (c) and (d) do not account for more cases being found.
Why this helps your RC score
Many RC questions are argument questions in disguise. "The author would most likely agree" is an inference question. "Which would the author see as a challenge to their view" is a weaken question. "The passage takes for granted that" is an assumption question. Once you can pick out the conclusion and the gap in a short argument, you can do the same with a 600-word passage.
What to do next
- For your next ten RC passages, write the author's conclusion and one assumption in a line each.
- Practise the negation test on every assumption option you meet, even the obviously wrong ones.
- Revise RC question types to see where these skills turn up in passage sets.
A note on dates and numbers. Exam patterns, vacancies and schedules change from year to year. Always confirm the current details in the latest notification on the Indian Institutes of Management website .
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