Logical reasoning PrepTest 107 · Section 3 · Question 10

Incorrect. The argument very much uses the commonality of self-interest in motivating all human action to say that it's the chief cause ("influence") on it, so it doesn't deny that.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Errors in Reasoning

Stimulus Summary:
Premise - Only self-interest motivates all human action
Conclusion - Self-interest is the chief influence on human action

Answer Anticipation:
What a short and sweet argument!

There are three elements here that suggest specific flaws, so let's start there.

First, the only premise uses conditional language—"The only" and "all." However, the conclusion isn't a conditional, and so it can't reverse/negate the logic. There's no conditional logic flaw.

Second, the argument discusses motive. However, it goes from a premise about motive to a conclusion about one, so there's no jump between action, motive, and outcome.

Finally, the conclusion is a comparison—self-interest is the "chief" influence on human action. Is that supported by the premise? The premise does establish that self-interest influences all human action, and no other motive does the same ("The only"). However, that doesn't guarantee it's the "chief" influence. It could be that it serves as a very minor influence on almost all human actions, and something else serves as the chief influence on 99% of such actions. In that case, the latter influence would certainly be more important than self-interest.

This argument jumps from how broadly something influences action ("all") to how important that influence is ("chief"). Let's find an answer highlighting that jump.

Answer Explanation:
The stimulus notes that only self-interest motivates all human action—so it's a particular influence on a class of events. It then assumes that this guarantees that it's the most influential factor—that it's influence outweighs any other influence. This answer correctly describes the faulty reasoning in the stimulus.

Key Takeaway:
Whenever the conclusion uses a superlative—best, chief, primary—check to see if similarly strong language is used in the premises. Here, the premise used strong language, but not when discussing how relatively influential something was—just how broadly that influence applied!

Incorrect. Both the premise and conclusion are fairly general, not necessarily limiting themselves to a single time. Or, if they do in using the present tense, then they both do, so there's no shift in time period here.

Incorrect. The argument never states that self-interest is the only influence on human action—just that it's the only influence on every single human action (leaving open the possibility that there are other influences on subsets of human action), and that it's the chief influence. Additionally, this answer discusses the influence being the chief influence ("paramount") as if it were the premise ("because . . . "), not the conclusion.

Incorrect. The argument doesn't contradict itself by bringing up a separate influence on all human action, or a situation where self-interest isn't an influence, so it doesn't undermine that claim.