Logical reasoning PrepTest 103 · Section 1 · Question 13

Valid

Cannot Be True Questions

Some people: Some politicians are rotten Author: Deceit is a part of being rotten → All effective politicians are rotten Effective politician → Deceitful Scrupulously honest → ~Effective politician

Cannot be True questions are all about contradictions - we need an answer that explicitly contradicts something from the stimulus. And when the stimulus involves conditional logic, there’s a common type of correct answer. But before we get to that, let’s break down the stimulus! First, the argument starts with what “[s]ome people” believe - an opposing point that likely won’t factor into the correct answer. After all, the only thing that would contradict this statement is that no one believes there are some rotten politicians in every group. From there, it moves into the Author’s conclusion - though we don’t care about it as a conclusion, since we’re told to treat all her statements as true. Here, then, we can diagram it out, as we did in the Summary, using “if” as the sufficient indicator. After that, we get another conditional, with “must” introducing a necessary condition. And then, finally, we get another conditional (“Someone” being used as “Everyone” here to introduce a sufficient condition). Looking at these statements, they don’t chain together, so we don’t have to do any work there. Instead, we should expect a common answer type in Cannot be True questions that have conditional statements - something that establishes the presence of a sufficient condition without its necessary condition. Let’s take a look.