A GMAT Critical Reasoning Pattern with Two New 2019 Official Guide Examples

Of the 31 new Critical Reasoning problems in the 2019 Official Guide books, two highlight a distinct and previously uncommon pattern of reasoning in cause and effect relationships. The problems are GMAT Official Guide 2019 #608 p.529 and GMAT Official Guide Verbal Review 2019 #155 p.148. These examples illustrate that one way to strengthen an argument relying on a cause and effect relationship is to show that interfering with the cause prevents or reduces the effect.

Consider the following example.

To alleviate the motion sickness George’s dog Rastro experienced during space flights, George’s veterinarian prescribed SpaceDoggieXR pills for Rastro. For two weeks, George faithfully gave Rastro two doses per day, as the vet specified. During this time, however, Rastro became listless and no longer wanted to play outside. George’s veterinarian hypothesized that Rastro is experiencing some of the common side effects of the SpaceDoggieXR medication.

Which of the of the following, if true, most strengthens the vet’s hypothesis?

A) Since Rastro’s SpaceDoggieXR regimen was discontinued two weeks ago, Rastro has become increasingly rambunctious and frequently wants to play outside.

Although this correct answer does not prove that the SpaceDoggieXR pills caused Rastro’s listlessness and lack of interest in playing outside, it does make it more likely that the medication was in fact the cause, since these symptoms disappeared when the medication was discontinued. An answer demonstrating that the argument is more likely to be valid is all we need for a strengthen question.

Alternatively, a weaken question could be set up as follows.

Which of the following, if true, most seriously undermines the vet’s hypothesis?

A) When George brought Rastro to the vet two weeks ago, Rastro licked the face of a sick dog in the waiting room.

This correct answer provides a classic alternative explanation - in other words, an alternative cause for the symptoms Rastro experienced. Specifically, perhaps Rastro contracted an illness from close contact with the sick dog in the waiting room. This possibility does not disprove that the SpaceDoggieXR medication caused the symptoms, but it does make it less likely, and that’s all we need for a weaken question. This answer is reasonable, even though we do not know for certain that the sick dog in the waiting room had a contagious disease and we do not know whether listlessness and lack of interest in playing outside are symptoms of the illness suffered by the sick dog in the waiting room. For weaken questions involving a cause and effect relationship in the passage, an alternative explanation is a common, but not the only possible type of correct answer. Be sure, however, not to look for an answer that says the effect doesn’t happen.

Critical Reasoning problems often employ the same types of logical patterns, dressed up with made-up content that may be designed to distract us from the underlying patterns. Familiarity with classic patterns will help in deconstructing many problems efficiently. If the Rastro example seems easy - that’s good! The idea is to be on the lookout for the same underlying pattern in a problem that presents a more complex story with a cause and effect, such as #608 on p.529 of the GMAT Official Guide 2019.

Stuart ParkGMAT