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Studying for a test? Prepare with these 3 lessons on Critical thinking.
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Fundamentals: Introduction to Critical Thinking

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(intro music) I'm Geoff Pynn. I teach at Northern Illinois University, and this is an introduction[br]to critical thinking. In this lesson, we're gonna[br]talk about three things. First, what is critical thinking? Second, what is an argument? And third, what's the difference between deductive and ampliative arguments? Okay, so what is critical thinking? Well, fundamentally, critical thinking is about making sure that you have good reasons for your beliefs. What does that mean? So suppose that you and your friend are talking about who's[br]gonna be at tonight's party. And she says to you, quite confidently, "Monty won't be at the party." You're not sure whether[br]or not to believe her, so it would be natural[br]for you to follow up by asking, "Why do you think so?" And there are a lot of different things that she might say in response. We're gonna talk about three possible answers she could give. First, she might say, "I can't stand him, and I want to have a good time." Second, she might say,[br]"Well, he's really shy, and he rarely goes to parties." And third, she might say, "He's in Beijing, and it's impossible to get here from[br]Beijing in an afternoon." The first response that she gives you does not give you a good reason to believe that Monty won't be at the party. The second reason,[br]though, is a good reason to believe that Monty[br]won't be at the party. If he's really shy and[br]rarely goes to parties, then it's probable that he[br]won't be at tonight's party. Similarly, the third reason[br]also gives you a good reason to believe that[br]Monty won't be at the party. If he's in Beijing, and[br]it's impossible to get here from Beijing in an afternoon,[br]then it's guaranteed that he won't be at the party. And when you notice things like that, when you distinguish between good and bad reasons for believing something, you're exercising your[br]critical thinking skills. So critical thinking is making sure we have good reasons for our beliefs, and so one of the essential[br]skills that you learn when you're studying[br]critical thinking is how to distinguish good reasons[br]for believing something from bad reasons for believing something. Now, it's worth saying something about how I'm using the term "good" here. I'm not using it to indicate anything having to do with morality or ethics. So it's not morally right or morally good to believe something on[br]the basis of good reasons. Similarly, it's not morally[br]wrong, or evil, or wicked to believe something on[br]the basis of a bad reason. Rather, here, what it is to[br]say that a reason is good is closely tied to the notion of truth. So a good reason for a belief is one that makes it probable, that is, it's one that makes the belief likely to be true. The very best reasons for a belief make it certain, they guarantee it. So why does this matter? Well, the reason that critical thinking is important is because,[br]since we're rational, we want our beliefs to be true. Rational people want to have true beliefs, and they want not to have false beliefs. And the best way to be[br]rational in this way is to form beliefs only when you find good reasons for them. Okay, that leads us to[br]our second question: What is an argument? Well, an argument is a set[br]of statements that together comprise a reason for a further statement. So, for example, we can consider one of your friend's responses[br]before as an argument. She's given you two statements, "Monty's really shy" and[br]"Monty rarely goes to parties," which together comprise[br]a reason for believing that Monty won't be at the party. The statements that are the reason, we call the argument's premises. So "Monty's really shy" is premise one, "Monty rarely goes to[br]parties" is premise two, and the statement that[br]those premises give you reason to believe, we call[br]the argument's conclusion. A good argument is one[br]in which the premises give you a good reason for[br]the conclusion, that is, the premises make the[br]conclusion likely to be true. In that case, we say that the argument supports the conclusion. Good arguments support their conclusions, and bad arguments don't[br]support their conclusions. So a key part of critical[br]thinking is learning to evaluate arguments to determine whether or not they're good or bad, that is, whether or not their premises support their conclusions. The red argument is the first response that she gave, two premises, "I can't stand Monty" and "I[br]want to have a good time." And the conclusion is "Monty[br]won't be at the party." And the third argument,[br]which we'll put in purple, consisted also of two premises, "Monty's in Beijing" and[br]"He can't get from Beijing to the party in time, so[br]he won't be at the party." Now, as I indicated[br]before, the first argument is not good, while the[br]purple argument is good. And here I can explain a[br]little bit more about why. If you consider what the[br]red argument's premises say, that your friend can't stand Monty, and she wants to have a good time, and think about their relationship to the conclusion of the argument, you'll see that those[br]statements don't make that conclusion any[br]more likely to be true. The fact that your[br]friend can't stand Monty and wants to have a good[br]time doesn't do anything to make it more likely[br]that Monty won't be there. It's simply unrelated to the conclusion. In the purple argument,[br]though, the premises, if they're true, they guarantee[br]the conclusion is true. So they make it very probable. The truth of the premises[br]guarantees the truth of the conclusion, and so[br]in the purple argument, the premises do support the conclusion. Now, it's worth pointing[br]out that the red argument, though it's bad as it[br]stands, could be made a good argument with the addition of some background premise. So, for example, if you found out that your friend was[br]the person who decided who was going to be invited to the party, then the fact that she can't stand Monty and wants to have a good time would give you a good reason to believe that Monty won't be at the party, because it would give you reason to believe that she didn't invite him. But as it stands, the[br]argument is not good. Those two premises[br]considered in themselves give you no reason to believe that Monty won't be at the party. Okay, our last topic is to distinguish two different types of arguments. So I'm gonna put up here, on the left, the orange argument, which is the second response that your friend gave, "Monty's really shy" and[br]"He rarely goes to parties." On the right we'll put[br]the purple argument, "Monty's in Beijing" and "He can't get from Beijing[br]to the party in time." Both of them have the same conclusion, "Monty won't be at the party." Now, as I said before, both of these are good arguments, they both do give you reason to believe the conclusion, i.e., both of them have premises which support the conclusion, but there's an important difference between the two arguments[br]that I want to point out. If you consider the purple argument, and think about what those premises say, you'll notice that if[br]those premises are true, if Monty's in Beijing,[br]and can't get from Beijing to the party in time, then it must be true that Monty won't be at the party. Those premises guarantee the conclusion. In such an argument, where the premises guarantee the truth of the conclusion, we call the argument deductive. In a deductive argument,[br]given the premises, the conclusion must be true. Just thinking about the information in the premises in a deductive argument gives you all you need[br]to deduce the conclusion. If you look at the[br]orange argument, though, you'll notice that that's not the case. In the orange argument,[br]even if those premises are true, the conclusion[br]might still be false. Even given that Monty is really shy and rarely goes to parties,[br]it's still possible that he'll get over[br]his shyness and suspend his policy of rarely going to parties, and unexpectedly show up. It's unlikely, but it's possible. So the truth of the premises[br]in the orange argument does not guarantee the[br]truth of the conclusion. Arguments like this, we call ampliative. In an ampliative argument,[br]the truth of the premises makes the conclusion probable[br]but doesn't guarantee it. Now, as I said, both of[br]the arguments are good. Ampliative arguments can often be very good arguments,[br]they're just not deductive. The premises don't guarantee[br]the truth of the conclusion. Now, when you're evaluating an argument, it can be important to know whether or not the argument is supposed to be deductive or supposed to be merely ampliative. If an argument is[br]supposed to be deductive, but careful consideration of the argument reveals that in fact the premises don't guarantee the[br]truth of the conclusion, if the conclusion could[br]be false even though the premises are true,[br]that's often a good reason to reject the argument as a bad argument. Whereas in an ampliative argument, to notice that the truth of the premises doesn't guarantee the[br]truth of the conclusion, is simply to notice that[br]it's an ampliative argument. If you were to object[br]to the orange argument by pointing out that,[br]still, the conclusion could be false, you'd[br]really be missing the point. In an ampliative argument,[br]it's taken for granted that the conclusion is not[br]guaranteed by the premises. Rather, what an ampliative[br]argument is doing is giving you reasons to think that the conclusion is probable. So knowing what type of[br]argument an argument is is essential to knowing which tools to use to evaluate whether or[br]not it's a good argument. And we'll talk quite a bit more about different tools for[br]evaluating both ampliative and deductive arguments in future lessons. Okay, so summing up this lesson. Critical thinking is making sure that we have good reasons for our beliefs, where we understand a good reason as one that makes the belief[br]probable, or likely to be true. An argument is a set of statements, which we call premises,[br]that together comprise a reason for another statement, which we call the argument's conclusion. And in a good argument, the premises support their conclusions, that is, the premises give you a[br]good reason for believing the conclusion, because[br]they make it probable. A deductive argument is[br]one where the conclusion is guaranteed by the premises.[br]If the premises are true, then the conclusion must be true. An ampliative argument[br]is one where the premises don't guarantee the conclusion, but they do make it probable. So they can still provide you with good reason for[br]believing the conclusion. Okay, so that ends this[br]introductory lesson. Subtitles by the Amara.org community