Logical reasoning PrepTest 147 · Section 1 · Question 15

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Errors in Reasoning

Stimulus Summary:
Book Ð Successful in business → Lucky
Rebuttal Ð Successful in business → Hard work
Conclusion Ð The book is wrong

Answer Anticipation:
First, we have to establish how we derived the conditional representation of what the book says. In stating that successful business people, without exception, have a certain feature, it's saying that all successful business people have that feature. "All" indicates a sufficient condition, so the book says that being lucky is necessary to success.

The argument attempts to rebut this by bringing up another necessary condition for success—hard work. However, this doesn't rebut the initial statement because there can be more than one requirement for something—success in business might require good luck and hard work. In using this conditional rule to rebut the initial one, the argument assumes that the book says that luck is enough, by itself, to guarantee success—in other words, it thinks the book says luck is sufficient. So this argument features an illegal reversal—the rebuttal treats the opposing point's necessary condition as if it were the opposing point's sufficient condition.

Another way of looking at it—if you say, "I need peanut butter to make a sandwich," and we say, "That's wrong, you also need bread," we think that you're saying peanut butter is enough to make a sandwich—in other words, it's sufficient.

Taking a step back, this argument features conditional language ("Anyone," "requires" "without exception"), and so a conditional logic flaw was the most likely issue with it, regardless of if you could figure out the specific version of that flaw.

Answer Explanation:
The book claims that luck is required for success. In raising a separate requirement for success as a rebuttal to that claim, the argument treats luck as sufficient for success. This answer reflects the flaw in the argument. Even if you didn't see the reversal, you still could have picked this answer since it's the only conditional logic flaw in the answer choices!

Key Takeaway:
Any language that denotes certainty—here, "without exception" and "requires"—is conditional in nature. When an Errors in Reasoning question features conditional language, the correct answer will usually refer to necessary/sufficient assumptions, even if you can't pin down exactly how it's messing it up. If there's conditional logic and you can't spot any other flaw, assume that that's what you're looking for.

Incorrect. Premises can be established as true without a citation on the LSAT, so this is almost never going to be a correct answer.

Incorrect. The premise is about hard work being required for success, and the conclusion is about luck and success—they're not repetitive, so this argument isn't circular.

Incorrect. This can be a tempting answer because it sounds like the argument is bringing up luck and hard work as a cause of success. However, first, the argument never actually establishes a causal relationship—just a requirement/conditional one. Second, even if we look past that and assume that luck and hard work are competing causes of success, the argument doesn't mix up what the cause and what the effects are—there's no discussion of success as causing luck or hard work.

Incorrect. The argument goes after the argument in the book, not the person who wrote it or the book itself. This answer would be correct if the rebuttal were about the book being poorly written, or the author being a failed business person.