Logical reasoning PrepTest 106 · Section 2 · Question 15

Valid

Parallel Reasoning Questions / Sufficient & Necessary Questions

Rhonda sees movie tomorrow afternoon → Paul goes to concert ~Ted agrees to go to concert → ~Paul goes to concert ~Ted agrees to go to concert Therefore - ~Rhonda sees movie tomorrow afternoon

This Parallel Reasoning question has conditional language all over it, so we should diagram it out and then find an answer that runs parallel to it. Here, the first sentence uses “only if” to introduce a necessary condition. In the second statement, we used “unless” as “if not,” leading to our diagram (you may have used a different method to get the contrapositive, which is fine). After these two conditionals (which chain together if you take the contrapositive of the first), we get a nonconditional statement that triggers the conditional, and then a conclusion that reflects the end of the conditional chain. So this is a valid argument that takes the form: A → B C → ~B C Therefore - ~A Note that, historically, the LSAT has treated “unless” as introducing the necessary condition and then negating the sufficient, so if that’s the case, we’d get an argument that instead looks like this: A → B B → ~C C Therefore - ~A The only difference is that the second statement here is the contrapositive of the second statement in the first anticipated form. Long story short, we’re looking for two conditionals that chain together and then are triggered to lead to a valid conclusion. If we get multiple answers that conform to that, we’ll need to dig in deeper with contrapositives.