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LSAT Logic Flaws: Correlation vs. Causation

Ever had this experience? Your gooberish buddy stumbles up to you, a couple drinks too deep, and spouts out an epiphany that (to him) rivals Einstein’s Annus Mirabilis. You and your LSAT-prepped mind, however, are not impressed. Something about the logic doesn’t sit right. It gives you an uneasy feeling deep in your gut — a sensation exacerbated by the PBR and stale pretzels sloshing around down there.

Let’s take an example. Say your friend — let’s call him Elliot — adamantly insists that when he stood up, Sexy Sadie looked over. He’s convinced that his standing caused her eyes to linger longingly on his portly physique and freshly-starched robin’s egg Polo.

You tell him, in accordance with your studies, that there are three methods by which we may seek to weaken a causal claim. The first is to check for “same cause, no effect.” If he stands again, and she fails to look over, then that would effectively weaken the notion of a causal relationship between the two (although he may insist that she was merely being coy).

Secondarily, we can look for “no cause, same effect.” If he is now sitting down, obstructed from her view, and she keeps looking in that general direction anyway, that could weaken the causal claim by suggesting that she’s looking over for some other reason.

Lastly, you present an “alternative explanation.” It all becomes so clear! She was never looking at Elliot. She was, of course, looking at you. This alternative explanation shatters Elliot’s causal claim, as it is no longer the case that his standing caused her to glance over. This narcissistic morass will likely self-perpetuate until an eye-rolling female compatriot points out that she’s wearing a Kobe Bryant jersey, and you both happen to be sitting beneath the TV airing the Lakers game.

There’s a fantastic scene from The West Wing in which President Bartlett criticizes CJ for committing this same fallacy. She mentions how poorly he performed in the Texas primaries after making an off-color joke, and Bartlett retorts that her tombstone will read “Post Hoc, Ergo Propter Hoc.”

“Post Hoc, Ergo Propter Hoc” is how you say “cause and effect fallacy” if you’re a pretentious asshole (or President Bartlett). Bartlett is critiquing CJ for assuming that because the two events are correlated, there is a causal relationship between them. But, he laments, “we were never going to win Texas.”

Cause and effect relationships are always suspect on the LSAT. These inferences are fallacious more often than not. Even outside the LSAT, when you think about it, causality is a very difficult thing to prove. This guy Hume wrote a good paper on it. When you encounter causal relationships on the LSAT, you should retain a healthy dose of Humean skepticism – just like you would for your buddy in the bar – and consider the aforementioned three ways to weaken causality.