LSAT Kung Fu Blog / Quick Hit: The Causal Flaw

Quick Hit: The Causal Flaw

Quick Hit: The Causal Flaw


Behold the awesome power of recognition (in which we circumvent the process of analysis by speedy categorization by type).

The causal flaw, as astute and keen-eyed visitors to this space well know, is the single-most-commonly committed error of reasoning on the test, by my count.

Here again, it rears its ugly head, and we will dispatch it with verve and a bit of dash.

We remember that there are three main ways that the causal flaw manifests; each of them is really a version of this assumption: That there wasn't any other cause for the effect.

1. Vanilla, no-other-cause-iness: The plain assumption that there wasn't something else that brought about the phenomenon (My pants are too tight, which I blame on my haberdasher's erroneous measurements. Maybe. Maybe bad measuring caused the pants to come out too tight. Then again, it might be the case that there's some other cause. Maybe I've been going pretty heavy on the Neverending Pasta Bowl at my local pit of gluttony and sadness Olive Garden Family Restaurant. Until I rule out my fatness as a cause, I can't blame the poor fit on my tailor).

2. Coincidence-as-cause-ishness. The assumption that the relationship between the two events was not just a coincidence (Home prices in my neighborhood have increased by nearly 10% since I moved in. Have the neighbors learned of my awesomeness and begun trying to cash in by selling their homes at a premium? Maybe. Maybe prices increased because I'm awesome. Then again, maybe the price increase had nothing to do with my recent move; the two events could be correlated without having any causal relationship. We can't say it was me that caused it until we rule out the possibility of coincidence).

3. Reverse-cause-ocity. The assumption that the causal relationship was not actually the other way around (Numerous studies have shown that nebbishy guys who marry supermodels are rich. Since I'm pretty nebbishy and desperately want to be rich, I will therefore figure out how to marry a supermodel. Boom. PROBLEM SOLVED. Again, maybe. Maybe marrying a supermodel somehow causes wealth. Then again, it may just be the other way around; maybe it's because they are rich that these nerds marry the supermodels. We can't say thing A caused thing B until we've ruled out the possibility that thing B instead caused thing A).

Here, we've claimed that the earthworm has caused the extinction of the goblin fern, because in places where there's less leaf litter, you find more earthworms and fewer goblin ferns. But do you see the possibility of another explanation? Yeah, me too.

So, yeah, maybe. Maybe the earthworm is causing the extinction, as this argument has claimed. But then again, maybe it's the other way around; maybe the disappearance of the goblin fern makes an area more attractive to earthworms.

In order to conclude that thing A (earthworms) causes thing B (extinction), we have to rule out the possibility that it's the other way around. In other words, to say the earthworms are the culprits is to assume that they do not move into an area as a result of the lack of goblin ferns.

Now check out answer choice (E)!


And also, seeing as this is a Necessary Assumption question, don't forget to perform your negate test; if (E) isn't true, and if worms actually do prefer to live where there are fewer ferns, then our argument becomes stupid; earthworms didn't cause the extinction, they were just attracted by it after it had already happened.

Boom. Problem solved.