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Intro to Critical Reasoning

Chris Lele
Lesson by Chris Lele
Magoosh Expert
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Welcome to the GMAT Critical Reasoning Introduction Video. In this video, we will talk about the question at a very high level. So if you are already familiar with the GMAT, a lot of this will be old news. However, if you are relatively new to the test, there may be some important tidbits here for you to learn. So first off, what does the argument look like?

Well, we're talking about the critical reasoning question. And it's made up of this argument here. Following the argument, there's a question step, and then, of course, five answer choices. So, basically, if you've ever opened up a GMAT prep book, this should look pretty familiar to you.

What perhaps not that common is how many questions show up on the verbal section that are critical reasoning questions. The answer is between 13 and 15 of the 41 verbal questions. This gives us about two minutes per question. And an important thing to note is, this differs for each person. You may find that you're very adept at critical reasoning, meaning you can finish these questions in less than two minutes and spend that time maybe on a harder part of the verbal section for you such as the reading passages.

Of course, for many, critical reasoning actually happens to be the most difficult of the three question types on the verbal. And, as long as you move through the other question types, meaning sentence correction and reading comp a little bit faster than two minutes, that can leave you some time for critical reasoning. Now, essentially, critical reasoning, as the name implies, tests your ability to reason.

But that is terribly vague. So, to give you some more specifics, here we have the idea that these arguments are made up of premises, which are facts, and conclusion, or the conclusion that can be drawn from these facts. To give you an example, let's take a look here at, all dogs have four legs. And Fido is a dog.

Therefore, Fido has four legs. What exactly is going on here? Well, there are a couple of facts that are stated. The first one is that all dogs have four legs. We take that to be the truth, there is no arguing with that premise, hence, it is a fact.

Second one is, Fido is a dog, Fido is not a cat, a pig, or some other animal. So on these two facts, we can therefore draw, notice the word therefore, a conclusion. And in this case, the conclusion is, Fido has four legs. Now, what's interesting about this is, this is testing a type of logic that's not actually found on the GMAT critical reasoning section.

Instead, we are gonna deal with what's called inductive reasoning, not deductive, or Fido reasoning that we saw a minute ago. The reason they're different is, with the Fido example, the conclusion flowed 100% from the facts. There was no room for doubt. So let's take a look here at something that is more an example of what you'll find on the GMAT, because it is inductive reasoning.

Marty has received an A on the last three algebra exams. He has studied three hours a night before each exam. The night before the final, Marty studies for three hours. Therefore, Marty will get an A on the algebra final. So what we have here, essentially, are premises, that part's not different. Premises are a fact, so we take these for granted.

However, the conclusion, though, is that he will get an A on the final. It is not air tight or 100%. How do we know this? Well, there are these unstated assumptions. That is, they're not actually expressed here, that make this conclusion not 100%, not air tight.

One of these assumptions is, the final requires the same amount of studying as a normal exam. Notice, he studied for three hours for the typical exams, so the assumption is he's gonna get an A on the algebra final by studying three hours. But wait a second. What if the final requires a lot more studying?

Another unstated assumption is, Marty is feeling well the next day. Clearly, if Marty is sick, he will not do so well on the final. Finally, we have another assumption here, Marty has studied all the material that will be on the final. Now, Marty could be in perfect health. He will only need three hours to study for this final, but maybe he didn't study the right thing.

And so any one of these assumptions threatens to make the conclusion not valid. So, if it's true that the final doesn't actually, requires a different amount of time to study, then wait a second. We can't draw the conclusion that he's definitely gonna get an A because he studied for three hours.

And so these unstated assumptions are very important to identify, because without them, the conclusion would not be 100% valid. So again, not 100% assured, there are many unstated assumptions, and that's what makes this inductive reasoning. So to kind of run through, again, the structure of the question, you have the premises, which are made up of these unstated assumptions, and that will lead to the conclusion.

From there, the questions essentially allow us to address these unstated assumptions. If you show that one of the unstated assumptions is actually true and it lends strength to the argument, then you strengthen the argument. But, if you address one of the assumptions and show actually this is the case and therefore it weakens the argument.

All of this flows from these assumptions. And so, for the next, next videos, we're gonna go in depth by attacking these assumptions for each of the question types.

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Critical Reasoning