Logical reasoning PrepTest 146 · Section 1 · Question 14

Incorrect. This answer is a reversal of what we're looking for. We need to know that someone who fails to keep a promise is failing to do something they ought to do, not the other way around.

Incorrect. First, this answer is too strong in stating that an unforeseen event is the only thing that can have an effect. Second, even ignoring that, the argument relies on an unforeseen event not excusing someone from an obligation—for the example to counter the principle, the person still ought to fulfill the promise despite the traffic jam.

Incorrect. This answer is the negation of the principle, and the Ethicist doesn't have to believe the negation in order to believe that the principle doesn't always hold true. A principle not holding true doesn't mean the negation of it; it means the sufficient condition is present without the necessary condition.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Strengthen with Necessary Premise

Stimulus Summary:
General principle Ð Ought to do something → Can do it
Counterexample Ð Promising to meet a friend but missing it because of an unforeseen traffic jam
Conclusion Ð The general principle is sometimes wrong

Answer Anticipation:
This argument establishes a general principle that the Ethicist intends to show isn't always true. In order to do so, she uses a counterexample, so it's important to understand how counterexamples work to disprove conditional statements, as the principle here is.

A conditional is a statement about a guarantee—if the sufficient condition is true, then so is the necessary condition. Therefore, in order to bring up a counterexample, a situation would need to be described where the sufficient condition is met but the necessary condition isn't.

In the counterexample provided by the Ethicist, the necessary condition definitely isn't met—the person can't meet up with their friend. However, the Ethicist never establishes that the sufficient condition is met. While the person made a promise, they were prevented from carrying it out for reasons out of their control. The Ethicist needs to establish that the promise still holds even when something like an unforeseen traffic jam comes up so that the example she raises can serve as a true counterexample and justify the conclusion that the general principle sometimes doesn't hold true.

Answer Explanation:
This answer establishes that the person in the counterexample raised by the Ethicist still had an obligation to meet with their friend despite the unforeseen impossibility of it. Therefore, it's an example of a time when someone ought to have done something that they couldn't do. If the obligation were relieved by the impossibility of it, then the example doesn't serve as a counterexample to the principle, and the Ethicist's argument falls apart.

Key Takeaway:
Counterexamples to conditionals need to highlight an example where the sufficient condition is present without the necessary condition.

Incorrect. The argument isn't about whether someone should have made a promise in the first place but whether someone who made one they can't keep "ought to" still do it.