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LSAT Arguments

This series of lesson articles will deal with LSAT Arguments. Handling LSAT arguments is key to half of the test, the two LSAT Logical Reasoning sections. 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

LSAT Arguments

Half of the test — the two Logical Reasoning sections — test your ability to read, analyze, and manipulate arguments. So what is an LSAT argument? It is not a quarrel or disagreement or a shouting match. An LSAT argument is a conclusion supported by premises and assumptions. Those are the three main elements of an argument.

Premise 1 + Premise 2 + …Premise n +

Unstated Assumptions =

Conclusion

Often, an author of an argument leaves something out. This is called an inference. There are two types of inferences, assumptions and conclusions. If the author leaves out a key piece of evidence (a premise), the inference is called an assumption. If the author leaves out the main idea and wants you to come up with it through your own thinking, the conclusion is inferred.

As we saw in the lesson series for LSAT Conclusions, the conclusion is the main point that the author wants to make. It the point the author wants to prove through her argument. Getting you to understand that main point is the reason the author made the argument in the first place. The conclusion is usually stated, but sometimes the author merely infers the conclusion. 

Since finding the conclusion is the initial step in unraveling an LSAT argument, let’s review some basic conclusion concepts within the structure of the following arguments. What do you think is the main idea of the following argument?

All of the G-rated movies made this year employ computer generated animation. Spy Chimps is G-rated. Therefore, Spy Chimps must employ computer generated animation.

What is the author trying to prove? What is the author trying to get at? The author wants to prove that Spy Chimps uses CG. Why? What is the evidence? Because all G-rated movies made this year employ CG animation and Spy Chimps is rated G. (Note: there is another key assumption here, that Spy Chimps was made this year.) Asking the question “why” can help you sort out the premise from the conclusion. The answer to the “why” will be the premises, or the facts that the author offers in support of her conclusion.

Occasionally, you might see an argument with more than one conclusion.

Watching Spy Chimps will burn your eyeballs. All of the G-rated movies made this year employ computer generated animation. Spy Chimps is G-rated. Therefore, Spy Chimps must employ computer generated animation. Since all computer generated movies are projected with radioactive lasers, Spy Chimps is projected with radioactive lasers. Watching any images projected with radioactive lasers will burn your eyeballs.

This argument demonstrates several principles of conclusions. First, you can have more than one conclusion in an argument. Second, the conclusion can appear anywhere in the argument. We get the main conclusion, “Spy Chimps will burn your eyeballs,” right at the top. Third, as ridiculous as the premises and conclusions are, you must just accept them to be true and see how the logic flows. If Spy Chimps is projected with radioactive lasers, and watching images projected with radioactive lasers will burn your eyeballs, then watching Spy Chimps will burn your eyeballs.

Since a conclusion can appear anywhere in the argument, how can you be sure which statement is the conclusion? There are some other clues that “Watching Spy Chimps will burn your eyeballs” is the conclusion to the first argument above. First, the chain of logic leads to this fact, even though it is stated at the beginning. The chain — if you reconstruct it on your own instead of using the order the author uses — is as follows: G-rated –> CG –> Lasers –> burning eyeballs. Second, what is the most important point the author wants you to take away? Probably the part about the burning eyeballs.

Sometimes you get lucky and the LSAT argument provides you with a clue word. The following list of clue words precede a conclusion.

  • Therefore
  • Thus
  • In conclusion
  • It must follow
  • Accordingly
  • Consequently
  • Hence
  • For that reason
  • So
  • Ergo
  • Then
  • Thereupon

Of course, there are many more signals to a conclusion that you will learn as you practice. Sometimes the author doesn’t use a clue word. Sometimes the author doesn’t even state the conclusion. For example, let’s look at an argument without a stated conclusion.

All apricots can fly. George Washington is an apricot.

The author didn’t say it, but the author is trying to lead you to the conclusion that George Washington can fly. The conclusion is an inference.

The next article in our series on LSAT Arguments will discuss the Structure of LSAT Arguments.

This Post Has 4 Comments
  1. There is a repeated mistake in this lesson that the conclusion is “George Washington is a mammal” where the conclusion should read “George Washington is warm-blooded”

    “All mammals are warm-blooded and George Washington is a mammal”
    Therefore, George Washington is warm-blooded (that he is a mammal is evidence!)

  2. Unfortunately, “All mammals are warm-blooded, and George Washington is warm-blooded. Therefore, George Washington must be a mammal.” is still not correct. As worldhiker said, I believe it should read, “All mammals are warm-blooded, and George Washington is a mammal. Therefore, George Washington is warm-blooded.”

  3. Thanks for your comment Vivien. The lesson was written correctly but you are right that the logic of that particular argument is flawed. This was deliberate. Most of the LSAT arguments are flawed in some way and that is why there are so many questions on the LSAT related to flawed arguments such as:

    The author assumes…
    The flaw in the above argument is most closely related to…
    Which of the following most weakens the above argument…

    We deliberately used a flawed argument so we could continue to use it to help with assumptions later on.

    But, since we’ve had several comments on this lesson, we decided this wasn’t the place to bring any extra confusion. So, we’ve rewritten the lesson to include all new argument examples that we hope reinforce the ideas of this particular lesson.

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