Strengthen, Weaken and Flaw — Practice

Question 1

Passage: Soon after the new coach arrived, the team began winning regularly. Therefore, the new coach is the reason for the team's success.
Which, if true, most weakens the argument?
(a) The coach is well qualified (b) At the same time as the coach, the team also signed a star striker who scored most of the winning goals (c) The team trains every day (d) The coach is popular with fans

Accepted Answer

(b) The team also signed a star striker who scored most of the winning goals.

This supplies an alternative cause for the wins, so the coach need not be the reason. Offering another explanation for the same effect weakens the causal conclusion.

Question 2

Passage: The town introduced a nightly curfew, and burglaries fell sharply that year. The mayor concludes the curfew reduced burglaries.
Which, if true, most strengthens the conclusion?
(a) The curfew was unpopular with some residents (b) No other anti-crime measure was taken that year, and nearby towns without a curfew saw no fall in burglaries (c) Burglaries are common in winter (d) The curfew begins at 11 pm

Accepted Answer

(b) No other anti-crime measure was taken that year, and nearby towns without a curfew saw no fall.

Ruling out other measures and adding a comparison group with no curfew and no fall makes it far likelier the curfew caused the drop, strengthening the conclusion.

Question 3

Passage: Every morning the rooster crows, and shortly afterwards the sun rises. Therefore, the rooster's crowing causes the sun to rise.
The reasoning is flawed because it:
(a) Relies on an unrepresentative sample (b) Treats one event's merely coming before another as proof that it caused it (c) Attacks the person rather than the claim (d) Assumes only two possibilities

Accepted Answer

(b) Treats one event's merely coming before another as proof that it caused it.

The crowing precedes the sunrise but does not cause it. Inferring causation from mere sequence is the post hoc (false cause) flaw.

Question 4

Passage: People who take multivitamins every day are, on average, healthier than those who do not. So taking multivitamins improves health.
Which, if true, most weakens the argument?
(a) Multivitamins are inexpensive (b) Health-conscious people who already eat well and exercise are the ones most likely to take multivitamins (c) Multivitamins are sold in most shops (d) Some people forget to take them

Accepted Answer

(b) Health-conscious people who already eat well and exercise are the ones most likely to take multivitamins.

This shows the healthier group may be healthier for other reasons (diet, exercise) and self-selects into taking multivitamins. The pills need not be causing the health difference, so the argument is weakened.

Question 5

Passage: A firm says its training programme raises productivity, noting that employees who took the training now produce more than those who did not.
Which, if true, most strengthens the claim?
(a) The trained and untrained employees had similar experience and output before the training began (b) The training lasts two weeks (c) The firm has many employees (d) Trained employees enjoyed the sessions

Accepted Answer

(a) The trained and untrained employees had similar experience and output before the training began.

If the two groups were alike beforehand, the later difference in output is more plausibly due to the training rather than pre-existing differences. Establishing comparable groups strengthens the causal claim.

Question 6

Passage: I have visited that city twice, and on both occasions it rained. The city must be rainy all through the year.
The reasoning is flawed because it:
(a) Draws a sweeping conclusion from too few observations (b) Uses a word in two different senses (c) Assumes the conclusion in a premise (d) Appeals to the opinion of the majority

Accepted Answer

(a) Draws a sweeping conclusion from too few observations.

Two rainy visits cannot establish the weather across a whole year. Generalising from such a small, possibly unrepresentative sample is the hasty-generalisation flaw.

Question 7

Passage: Either we cut the school's music budget, or the school will go bankrupt. We certainly cannot let the school go bankrupt. So we must cut the music budget.
The reasoning is most vulnerable because it:
(a) Attacks the musicians personally (b) Presents only two options when others (such as new funding or other savings) may exist (c) Relies on an anonymous authority (d) Restates its conclusion as a premise

Accepted Answer

(b) Presents only two options when others may exist.

The argument assumes the sole choices are cutting music or bankruptcy, ignoring possibilities like raising funds or saving elsewhere. Forcing a choice between only two options is the false-dilemma flaw.

Question 8

Passage: This newspaper is the most reliable in the country, because it never prints anything false. And we know it never prints anything false because, after all, it is the most reliable newspaper in the country.
The reasoning is flawed because it:
(a) Generalises from one example (b) Uses its conclusion as the support for its own premise (c) Confuses correlation with causation (d) Appeals to popularity

Accepted Answer

(b) Uses its conclusion as the support for its own premise.

The claim 'most reliable' is supported by 'never prints falsehood', which is in turn supported by 'most reliable'. The argument assumes what it sets out to prove — circular reasoning.

Practice — Strengthen, Weaken and Flaw

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