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Structure of LSAT Arguments

This article is the second in a lesson series on LSAT Arguments. This article will discuss the structure of LSAT arguments: the parts and pieces of LSAT arguments, how the work and why they are there.

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

You may recall that the structure of LSAT arguments contains three main parts: premises, assumptions and conclusions. We’ve talked about conclusions in the previous article and we’ve covered them in a separate lesson series on LSAT Conclusions, so let’s jump into the other pieces of the structure of LSAT arguments.

Premises (Evidence)

The premises of an argument (often referred to as evidence) are the facts the author offers in support of her conclusion. For the most part, do not argue with the premises. Accept all premises to be 100% true, even if you know them to be false. You are rarely if ever asked to strengthen or weaken a premise, so don’t waste time considering their veracity. Assume they’re true and see what follows. Again, the premises answer the “why” of the conclusion.

All school children chew gum, and Stacey is a child in school. Therefore, Stacey must chew gum.

Why does Stacey chew gum? Because she is a child in school and all school children chew gum.Try it the other way around — it just doesn’t work. Why do school children chew gum? Because Stacey is a child in school? Because Stacey chews gum? You see, those logic flows don’t make sense. The answers to the “why” are the premises.

Just like conclusions, premises also have clue words. The following words often precede a premise:

  • Because
  • Since
  • As
  • On Account of
  • For
  • By reason of
  • Considering
  • In as much as

Of course, not all authors give their premises away so easily. In fact, some premises are hidden, or inferred. These hidden premises are called assumptions and are the most important element in an LSAT argument.

Assumptions

Assumptions, or unstated premises, are the key to the LSAT. The majority of the questions will ask you to do something to the assumption, even if the question doesn’t use the word “assumption” explicitly. Some questions ask you outright to identify the assumption. Some ask for the inference, which is usually the assumption and only occasionally the conclusion. If a question asks you to strengthen or weaken the argument, you almost always find evidence for or against the assumption. Understanding the assumption is the path to a high score.

The assumption is an unstated premise. We left out one of the key premises in the following argument.

Redlands coffees are locally roasted blends. Smittee’s must be locally roasted.

The assumption is the third and necessary part of the argument. If the premises and conclusions are true, what else must be true? What is the argument based on? You can see that there is a step missing. Test Sherpa uses a method we call bridge building to find assumptions. Take a look at what is dissimilar in the premise and the conclusion. Those are the pieces you need to bridge. In this simple example, you don’t need to bridge locally roasted to locally roasted because those ideas are the same. What you need to bridge is Redlands coffees to Smittee’s. So the assumption must be that Smittee’s is a Redlands coffee. Now lets get picky and point out that this is really two assumptions in one, an assumption about Redlands and an assumption about coffee. Let’s restore the missing premise.

Redlands coffees are locally roasted blends. (Smittee’s is a Redlands coffee.) Smittee’s must be locally roasted.

The Red Flag

The assumption is the weakest link in an argument. Take a look at the following argument that is clearly flawed. In fact, if you’ve read the article on logical flaws, you would know that the flaw involved here is a common one called denying the antecedent.

If you listen to David Hasslehoff songs, you will be accepted into Harvard Law. I guess I won’t be going to Harvard.

The only way for the author to get to the conclusion of “I guess I won’t be going to Harvard,” is to deny the first part of the argument. In other words, the author’s conclusion is a clever way of saying that he doesn’t like to listen to David Hasslehoff. But it’s bad logic. The assumption involved is that he doesn’t listen to the ‘Hoff but there are probably hundreds of other ways to get into Harvard that he hasn’t considered. Like scoring high on the LSAT, for example.

As you read most of the arguments in the Logical Reasoning section, a “red flag” will pop up in your mind. Think of how you would rebut the argument. Think about the weak link or gap. That red flag is an unanswered question. That red flag points to the assumption. When you read the argument and say, “hey, wait a second, there are more ways than one to get into Harvard,” and you are on your way to finding the assumption in a very fast, intuitive manner.

In the next article in this lesson series, we will practice finding LSAT assumptions.

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