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Finding LSAT Assumptions

This article is the third in a lesson series on LSAT Arguments. This article will demonstrate techniques for finding LSAT assumptions. Assumptions are the parts of the argument that the author left out but must be intended by the author given the premises and the conclusion.

This lesson series covers the following articles:

LSAT Arguments: An Introduction
Structure of LSAT Arguments
Finding LSAT Assumptions
Logic on the LSAT: Two Types
Practice LSAT Arguments

We have an entire lesson series on LSAT Assumptions, so you’ll get plenty of practice identifying the assumptions. Let’s test out the basics here so you can better understand the LSAT argument structure and how to find LSAT assumptions. In each of the following examples, read the argument and identify the conclusion and premises. Then guess at the assumption before you read the answer.

I have plenty of gas in my car, so it will start right up.

What’s the main idea? That the car will start right up. Why? Because I have gas in the car. What is the red flag that goes up in your head? Aren’t there other reasons why a car may not start than just gas or no gas? Of course there are. So the assumption must be that the only reason a car might not start is if it has no gas.

Here’s how you do it. Identify the conclusion and the premises. Then try to phrase any assumptions you see in the argument before you read the explanation. Try it on your own with the following.

Last year, charitable contributions to churches went up by 15 percent. That goes to show that more people are attending church this year.

What’s the main idea? More people are attending church this year. Why? Charitable contributions to church were up last year. What’s the problem with that, the red flag? Couldn’t the same people who attend contribute more? Couldn’t there be an increase in people who donate to a church but never go? So, just because contributions are up doesn’t mean that more people are attending church. Also, just because we measured something last year, doesn’t mean we can necessarily count on an effect this year. So what are the assumptions? The increase in contributions is not due to an increase in contributions by people who already attend the church. Also, that an increase from last year is relevant and will predict behavior this year. 

Try it again on the following argument. Identify the conclusion and the premises. Then try to phrase any assumptions you see in the argument before you read the explanation.

Japanese schoolchildren spend a significant portion of their day studying mathematics. In contrast, American schoolchildren spend several hours a day studying mathematics. Japanese students typically score higher on entrance tests to graduate school than American students. If America wants more students to get into graduate school, its schoolchildren need to spend more time studying math.

What’s the main idea or conclusion? American schoolchildren should spend more time studying math in order to get into graduate school. Why? Japanese children spend a significant part of their day studying math, and Japanese students score higher in entrance tests. What is the red flag? There are so many, where should we begin? 

First, American kids already spend “several hours” studying math. Is that less significant than the time the Japanese kids spend, and would an increase make a difference? Second, the high score on an entrance exam does not necessarily mean a higher math score. Finally, and this gives comfort to pre-law students everywhere, the score on an entrance exam is only part of why a person is accepted into graduate school. 

Obviously, with so many red flags, this argument assumes a lot. First, an increase in the amount of time American kids are already studying math would lead to higher graduate entrance exam scores. That’s a huge logical leap. Second, American students couldn’t sufficiently increase their exam scores in other areas besides math. And finally, a high exam score is all you need to improve your chances of getting into grad school, exclusive of personal statements and work experience.

You can learn more about LSAT assumptions in our LSAT Assumptions series. The next article in this LSAT course is about the two types of logic on the LSAT.

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