Logical reasoning PrepTest 148 · Section 1 · Question 13

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Errors in Reasoning

Stimulus Summary:
Purpose of laws to make people happy → Basis for criticizing and writing laws
Therefore: not Purpose of laws to make people happy → not Basis for criticizing laws
Therefore: Current laws are legitimate because they're laws

Answer Anticipation:
As soon as you see that conditional language kicking off this argument, you should start thinking about a conditional logic flaw (illegal reversal or negation). That second sentence uses both conclusion language ("Hence") and conditional language ("if . . . "), so we should check to see if it makes an illegal inference from the initial conditional.

And it does—it takes the premise conditional and negates it as the conclusion. That's an illegal negation, so we should look for conditional logic flaw answers.

Since the argument also includes another conclusion, we should check for assumptions there, as well, as a correct answer could deal with that flaw instead. Here, the argument jumps from stating that if the purpose of laws isn't to make people happy, then we can't judge laws, and thus they must gain legitimacy not from analyzing them but from them being laws. That assumes that without a basis for evaluating laws, they can only gain legitimacy from being laws.

Either flaw could be highlighted in the correct answer, so let's dive in and see which shows up!

Answer Explanation:
This answer highlights a conditional logic flaw. While it points out an illegal reversal, reversals and negations are contrapositive of each other, so this describes the flaw in the logic. The premise establishes that laws being meant to contribute to happiness is a sufficient condition, but it concludes that a lack of it will ensure the lack of the other condition—in other words, it treats it as necessary.

Key Takeaway:
As soon as you see conditional logic in an Errors in Reasoning question, you should start to look for illegal reversals and negations. And while they each have answer choices that are more commonly associated with them individually, there's always a chance that the correct answer will describe one as the other since they're logically equivalent (they're contrapositives of each other).

Incorrect. While the main point is causal in nature and it is based on a correlation, that correlation isn't between elements in the causal relationship, so this isn't a correlation/causation flaw.

Incorrect. The stimulus reuses "purpose," but in both the premise and intermediate conclusion it means the reason the law was enacted. It does go from talking about criticizing laws to evaluating them, but they're essentially synonyms. There's no shift in meaning here.

Incorrect. There's no discussion of how the world should be in the stimulus.

Incorrect. The stimulus always discusses laws as being a group of distinct laws all of which the statements apply, so there's no shift from premise to conclusion.