You’ve probably heard this oft-repeated mantra of LSAT studying: no outside knowledge on the LSAT!

And yet, once you get into the nitty-gritty, it seems a little more complicated – after all, the LSAT doesn’t spell everything out for you. Assumptions that are and are not permissible is a continual source of confusion for my students, which has led to many an in-depth discussion. I’m getting tired of having to settle these disagreements via one-on-one cage match, so I wrote this post: the definitive guide to permissible assumptions on the LSAT. (It’s a two-parter, so make sure to check out the LSAT blog next week for advice on what you CAN assume.)

Part I: What you’re NOT allowed to assume on the LSAT

The LSAT doesn’t require any specialized knowledge of certain subjects, and in fact, if you have specialized knowledge you should probably try to temporarily forget it.

For instance, in the June 2008 LSAT (Section 2, Question 24), there’s a question about cows contributing to global warming because they produce methane. (LSAC delicately avoided mentioning that this methane is released in the form of cow flatulence.) One of the wrong answers for this question says that cow feed contains an abundance of carbon and hydrogen, the elements that make up methane.

But slow down there, pardner. Even if you know it to be true that consuming food with these elements would lead to methane production, you can’t assume that’s the case here. We know that cows are consuming the component parts of methane, but we can’t assume anything beyond that.

One more example, from the June 2009 LSAT (Section 4, Question 9): In this question, the physician says that, although his country and country X face the same causes of stress-related ulcers, his country has much fewer prescriptions for ulcer medicine. Thus, his country has much fewer ulcers per capita.

The argument is making an assumption that the number of prescriptions is indicative of the number of actual ulcers. The problem is that we don’t actually know whether that’s the case. Maybe someone who has an ulcer in the physician’s country won’t be able to get to a doctor to get a prescription, or maybe the people in that country have a culture that discourages getting prescriptions for uncomfortable but non-life-threatening conditions like ulcers.

So we can’t assume that someone is going to seek treatment for an ulcer. That probably means we can’t assume anyone will seek treatment for anything, right? Not so fast!

I probably sound like your mom right now, giving you this extended list of things you can’t do. Next week I’ll break down the (short) list of things you can assume, as well as the nuances of ulcer treatment, so stay tuned!