San Francisco LSAT Instructor Blog

One of the most frequently used kinds of questions in the arguments sections of the LSAT is the assumptions questions, in which you are supposed to figure out, which assumption out of the four or five possible answers the argument depends on.  The most common reason for the wrong choice of answer out of the two competing, seemingly valid answers is the following: one of the answers that seems to be correct is not the right answer because, while it might be the general assumption that’s necessary for the argument to be valid, it’s not an assumption which is necessary to support that particular argument.

For example, consider the following argument:

“David decided to go to Starbucks instead of Peet’s Coffee because he wants to lose weight. “

The correct answer to the assumption question would probably look like this:

Starbucks serves a lower-calorie food/drinks that Peet’s.

The writers of the LSAT will try to mask the correct answer with another option that will generally look like an assumption that’s also needed, such as: the assumption that there are both Starbucks and Peet’s are located in your area; or that you have the money to pay for what they sell, etc…

When you are faced with those competing answers, remember this very important fact: you are not asked to just find a valid assumption in the argument, as there are many of those, including such facts as that you are able to walk, that you are not allergic to coffee, that you can speak the language and explain what you need to the coffee barista, etc…  You are asked to identify the assumption on which that specific argument depends. All the other assumptions are generally necessary for just about every argument, but they are not needed to link the permise and the conclusion of the specific argument that you are dealing with. To link loss of weight with the choice of coffee store you are going to go to in the above example, you only need one assumption: the assumption that one store’s products are less fattening than the other’s. The rest of the possible assumptions, while theoretically necessary, are not necessary to connect the two parts of that specific argument.

Keep this tip in mind, and it will be of great help to you when you are dealing with the so common assumption questions in the arguments section of the LSAT.