Causality on the GMAT

One of the most common types of arguments you’ll see on the GMAT will be cause-and-effect. A cause-and-effect argument can best be thought of as one arguing that a certain fact or phenomenon directly brings about another one. One of the pitfalls of any causal argument is that the seemingly apparent causal connection might not actually exist.

Let’s take a look at a typical causal argument to see this issue in action:

“Most people who smoke cigarettes suffer from depression. Therefore, cigarette smoking causes depression.”

This is representative of the type of erroneous reasoning you’ll see on GMAT Critical Reasoning. The premise takes a correlation between two events (cigarette smoking and the incidence of depression), and from that concludes that one of these events causes the other. But this conclusion is not necessarily true. Why? Because anytime you have a causal argument, there are 3 different connections that you must consider, all of which will have some validity depending on the premises.

Possibility #1 is that phenomenon X causes phenomenon Y. In the above example, this would be “Cigarette smoking causes depression.”

Possibility #2 is that phenomenon Y causes phenomenon X. In the above example, this would be “Depression causes cigarette smoking.”

Possibility #3 is that both phenomenon Y and phenomenon X are both caused by some outside variable. In the above example, one possibility would be that “Obesity causes depression and cigarette smoking.”

Because all three of these connections are equally plausible, the conclusion that cigarette smoking leads to depression is flawed. How could that conclusion be strengthened? One way would be to eliminate one of the other possibilities listed above, as in the following statement: “Research shows that people who have been depressed for a long period of time are no more likely to smoke than non-depressed people.”

This statement reduces the possibility that depression causes smoking and, in so doing, strengthens the conclusion that the connection between cigarette smoking and depression implies that cigarette smoking causes depression. Though still not airtight, the conclusion now gains more plausibility.

So next time you’re practicing Critical Reasoning, pay attention to any causal arguments you see, and ask yourself whether the three possibilities listed above are all equally likely.