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Course: LSAT > Unit 1

Lesson 6: Logical Reasoning – Articles

Types of evidence

Types of Evidence

It can be useful to separate and identify different types of evidence used in an argument to support a conclusion.

This can help you avoid getting “lost” in the words; if you’re reading actively and recognizing what type of evidence you’re looking at, then you’re more likely to stay focused.
Different types of evidence are often associated with specific types of assumptions or flaws, so if a question presents a classic evidence structure, you may be able to find the answer more quickly.

There are many ways to support a conclusion; we’ll walk through some of the most common ones that you may see on Test Day.

Common Evidence Types

Let’s consider the following claim:

Conclusion: Paola is the best athlete in the state.

What types of evidence might support this claim?

Examples as evidence

An example provides evidence that is meant to support the conclusion. What’s an example of Paola being a superior athlete?

[Paola is the best athlete in the state.] After all, Paola has won medals in 8 different Olympic sports.
Paola beat last year's decathlon state champion on Saturday, so [she is the best athlete in the state].

What others say

Drawing on what others say (sometimes called an “appeal”) as evidence is a fairly common way for someone to attempt to prove a point.

[Paola is the best athlete in the state.] We know this because the most highly-acclaimed sports magazine has named her as such.
Because the population voted Paola the Best Athlete in the state in a landslide, [it would be absurd to claim that anyone else is the best athlete in the state].

Top tip for flaws and assumptions: Ask “Is it enough?” When you see an appeal being made, take the time to think about whether the object of the appeal is relevant and useful. For example, if an arguer makes a scientific claim but appeals only to one scientific expert, there’s a lot of room to attack that argument (if it’s necessary to).

Using the past

When an arguer uses the past to justify a conclusion, it’s often with the assumption that things haven’t changed since that past.

[Paola is the best athlete in the state.] She must be, since she won the state championships last year, two years ago, three years ago, and four years ago.

Top tip: When you see an arguer use the past to justify a prediction (or the present, as in our example), ask yourself, “Is it possible that things have changed, and that that past evidence is no longer relevant?”

Analogies

Sometimes an arguer will use an analogy as evidence, by describing a similar but unrelated situation as support.

[Paola is the best athlete in the state], because she won the most athletic awards. Look at Jude, who's currently the Best Chef in the State because he won the most cooking awards.

Top tip for flaws and assumptions: Ask “are they really the same?” When the arguer makes an analogy, always check to ensure that the two situations being compared are actually logically comparable. If they aren’t and you’re solving a flaw question, then you already have your answer as to the flaw! And if you’re tackling a necessary assumption question based on an argument employing an analogy, then your necessary assumption might be that the two situations are similar enough to be compared.

Generalizing from a Sample

Sometimes an arguer will use a sample to make a generalization:

[Paola is the best athlete in the state], because she won every local tournament in every spring sport.

Top tip: Pay attention to samples on the LSAT. In the example above, you can see a shift from the sample to the conclusion. The evidence addresses every local tournament in every spring sport, and then the arguer concludes that Paola must be the best athlete in the state.

When you see a sample, a good first step is to take a quick peek to confirm whether the sample is appropriate; in other words, ask yourself, “Is the group of things/people discussed in the evidence representative of the group of things/people discussed in the conclusion?”

Common Rebuttal Structures

You’ll also see rebuttals on the LSAT, with commonly-used evidence types to support those rebuttals.

Counterexamples

Counterexamples are examples used to refute (or “counter”) someone else’s opinion. Usually, it'll be when one arguer makes a generalization, and then another arguer presents a specific example that refutes that claim. Consider the following claim:

Robert: Everyone's favorite food is pizza.

A counterexample might look like this:

Brianna: That's not true. My favorite food is paella.

In other words, in making a counterexample, the arguer produces a specific example that hurts the other arguer’s or arguers’ reasoning.

Alternate Possibilities

A speaker may rebut another speaker by pointing out a different cause, effect, reason, etc. than the one being cited. To give just one example, if the first speaker believes that X will lead to Y, you may see the second speaker question why X couldn’t lead to Z instead.

Other types of argument structures

Conditional

These are arguments that draw conclusions based on conditional relationships. Conditional relationships are true/false relationships between different ideas: if one is true, then another has to be true as well. These are absolute: they hold always and in all cases. They can be combined to imply other general relationships, or they can be applied to individual cases to draw specific conclusions.

Top tip: When in doubt, draw! Many students find it helpful to diagram the evidence when there’s a substantial number of conditional relationships present. For example,

The Penguins won’t win unless the Flyers make a big mistake, and the only way that the Flyers will make a big mistake is if the coach is tired that day. The coach is never tired on Fridays, though.

could be diagrammed as:

Penguins win $\to$ ‍ Flyers make big mistake
Flyers make big mistake $\to$ ‍ coach tired
Friday $\to$ ‍ coach is not tired

Visit the Logic Toolbox in the Lessons area for help with conditional logic!

Causation based on correlation

These arguments reach a conclusion that A causes B. The support often involves statements about correlations: observations of two things happening at the same time. Look for language that shows that one thing directly affects another:

The flood last week was due to climate change.

This kind of culture fosters resentment.

The incorrect prescription was responsible for the patient's death.

Top tip: A very common way to weaken a causal argument is to identify an alternate cause for the effect that is observed or provided.

For example:

I put a new mattress cover on my bed last night, and I sneezed all night. So my new mattress cover must be making me sneeze.

This is a causal argument that supposes that the new mattress cover (and not anything else) is making the speaker sneeze. A classic way to weaken this argument is to show that something else (for example, a virus or increased pollen in the air) is causing the sneezing.

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Mishara Davis
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I'm typically only able to answer about 16 questions on LR sections. Tips on improving speed while maintaining accuracy?
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Roger Hans
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Pointing out (ARC) Alternative, Reverse or Coincidence may be attributed to the effect is an effective way to weaken argument.
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K A
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There are a lot of question types in LR. What order should I master these types?
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Robt DePasquale
Posted 5 years ago. Direct link to Robt DePasquale's post “Coach is never tired on F...”
Coach is never tired on Friday.

Does that mean that the game is taking place on Friday? Or could it be another day.
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ashkan.2dar
Posted 4 years ago. Direct link to ashkan.2dar's post “Thank you for the compreh...”
Thank you for the comprehensive explanations. English is not my native language and I do have a problem with fast-paste reading in English. I have been practicing LR section for a while now. I still make a lot of mistakes when answering questions for the first time. But when I go back and read it without timing, I can quickly recognize my mistakes, analyze the questions, and find the loopholes between premises and conclusion that I initially was not able to detect. Do you have any recommendations for ESL test takers?
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- Lei Liu
  Posted 2 years ago. Direct link to Lei Liu's post “practice more I guess”
  practice more I guess
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haanahaaron
Posted 2 years ago. Direct link to haanahaaron's post “What is the LSAT referrin...”
What is the LSAT referring to, when using the word generalization? Is it referring to conclusion, support, or entire argument?
For example, Common Rebuttal Structures, in topic counterexamples
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