Is It Ever Valid to Attack a Premise in a Logical Reasoning Question?

[Auntrunt]

Hi everyone,

I've come across a few Logical Reasoning questions where the argument seems to rely on a premise that feels questionable or overly broad. I know we're generally supposed to accept all premises as true in LR questions, but is it ever valid—or even useful—to mentally "challenge" a premise to better understand the flaw or assumption?

For example, in some flawed arguments, the premise itself might contain an ambiguity or sweeping generalization. Does PowerScore recommend treating that as part of the flaw analysis? Or is it always better to focus on the logical link between premise and conclusion, regardless of how strange the premise may seem?

Curious how others handle this—especially in questions involving causality or surveys/statistics. Thanks!

[Jeff Wren]

Hi Auntrunt,

First, it's important to distinguish between Flaw questions and Weaken questions, as the flow of information and how they are solved is different with these two question types.

For Weaken questions, you are looking for an answer that brings in new information that hurts the argument. Attacking a premise is one acceptable way to weaken an argument. (In "The Logical Reasoning Bible," this is even listed as one of the ways to weaken an argument in the chapter on Weaken questions.) However, because an answer that weakens a premise is often easier to spot, the test makers use this way of weakening arguments less often. Also, answers that weaken a premise usually don't directly disprove the premise itself, but instead offer additional information that calls the relevance or accuracy of the premise into question.

For example, imagine the following argument.

A recent study showed people who stretch before exercising were 50% less likely to be injured than people who do not stretch before exercising. Therefore, stretching before exercising helps prevent injuries.

One answer that would weaken this argument might be something like:

Another recent study showed no difference in the likelihood of injuries between people who stretch before exercising and people who do not stretch before exercising.

While this answer doesn't directly disprove the premise of the argument, it does cast doubt on it by providing conflicting data.

With Flaw questions, you do need to consider the relationship between the premises and the conclusion to understand the flaw. While the flaw may sometimes appear to be occurring in the premises, it is usually how the conclusion is incorrectly drawn from those premises.

For example, imagine the following argument.

A survey of American business owners found that 85% were against raising the minimum wage. Therefore, most Americans do not want to raise the minimum wage.

This argument contains a survey error involving an unrepresentative (and almost certainly biased) sample. It would not be surprising that many business owners would be against raising the minimum wage since this would likely increase the expenses of their businesses and decrease their profits. On the other hand, many employees making minimum wage would probably feel differently, as raising the minimum wage would increase their pay.

It may appear that the flaw occurs in the premise because they surveyed the wrong group of people. However, the only reason that the survey is unrepresentative is because the conclusion is about "most Americans" rather than "most American business owners." If the conclusion had been about "most American business owners," then the group surveyed would not have been unrepresentative. In other words, the flaw here doesn't really appear just in the premise or just in the conclusion, but in how the conclusion differs from the premise.