 Hello, this is the third in a sequence of videos to help with critical thinking and this video is going to be all about assumptions. Now, first of all, it's very important to understand that the word assumption is used with the precise technical meaning in critical thinking that differs from the way it's used in ordinary speech. In critical thinking, an assumption is a missing reason. It's something that hasn't been said. But at the same time, an assumption is something that's needed for an argument to work. Now, if you think about this, this is different from the way people usually use the word. Normally, by an assumption, people mean something that they're taking for granted, but it could well be something that they've actually said. In critical thinking, we use the word assumption to talk about something that's missing, but that would have to be true or else the argument doesn't work. So it's something that the author must believe, but that they haven't said. And you can see from that definition that assumptions are going to be something that's really interesting in an argument because assumptions have to be true for the argument to work. And so therefore, if they're not true, the argument falls apart. At the same time, there's something that hasn't been said, and so perhaps the author hasn't really thought about them. So by thinking about assumptions, we're thinking about things that the author hasn't really considered, but which are very important because whether they're true or false has a big effect on the argument. Okay, now in order to explain a bit more about what I mean by assumptions, we're going to think a little bit about polar bears. Okay, now here's a very simple argument that I'd like to think about. The argument says Mr. Nickel needs to watch out. There's a polar bear behind him. So this is a really simple argument. It's got a conclusion. I need to watch out for the reason there's a polar bear behind me. But I'd like to see if you can think of something that's assumed here, something that hasn't been said, but that would have to be true if we're going to be able to say that I need to watch out. So I suggest you pause the video for a bit and try to think of something that's assumed here. Okay, well one thing that would mean I don't really need to watch out is if there's a big glass wall between me and the polar bear, for example if the polar bear is actually in an aquarium. So an assumption is that there isn't a big thick wall between me and the polar bear. That hasn't been said, but it needs to be true otherwise I don't need to watch out. Another thing that would mean I don't need to watch out is if it's just a baby polar bear that's sort of half asleep. So another assumption is that the polar bear isn't a baby. Again, that's something that hasn't been said, but it needs to be true otherwise the argument doesn't work. We can't say that I need to watch out. It's assumed that the polar bear is close behind me. Of course if I stand facing in a certain direction then I've got my back to the north pole and there will be plenty of polar bears behind me a long way off in Svalbard, but I don't need to watch out. So we need to assume that the polar bear is close behind me. We're assuming that the polar bear isn't a cowardly polar bear that's afraid of me because if the polar bear were afraid of me then obviously I wouldn't need to watch out. It'll probably run away. You have to assume that it's a real polar bear because obviously if it's just a stuffed toy polar bear then I don't need to watch out. We're assuming that the polar bear is alive because again if it's dead there's no need to watch out. We're assuming that it's not a stuffed polar bear inside a glass cage. We're assuming that I'm not being protected by some men with a massive gun ready to take down the polar bear in case it gets too close to me. And we're assuming that I'm not being protected by a big robot with powerful machine guns as arms. And finally this picture isn't meant to correlate with an assumption it's just a nice picture of polar bears. So I hope that gives you the sense of what assumptions are. Just to remind you they're missing reasons things which nobody has said. But on the other hand they're needed for the argument to work. If they weren't true then the argument would fall apart. Now there's actually a really good test to make sure whether something is assumed or not and that's called the negative test. First of all I need to say what I mean by the negative of a statement. You negate a statement by writing it's not the case that in front of it or it's not true that at the start. And now the negative test works like this. The negative of an assumption prevents the conclusion from being drawn it ruins the argument. So if you take an assumption and you negate it it destroys the argument. And that's how you know that the original thing was an assumption. Let's look at an example of this. Before we were looking at polar bears now let's look at gorillas. Here's an argument about gorillas. Gorillas are highly endangered so we should try to save them. Okay now it might be a good idea to pause the video again and try to think of some assumptions that that argument makes. Okay well here's a couple of possible assumptions. First of all saving gorillas is desirable. And secondly we should try to save all endangered species. So let's test these one at a time using the negative test. First of all let's focus on saving gorillas is desirable. The first step in the test is to negate that. So we would say it's not the case that saving gorillas is desirable. And we can simplify that to just saving gorillas is not desirable. Now we combine that with the original argument to get something like this. Gorillas are highly endangered saving gorillas is not desirable but we should try to save them. And I hope you'll agree that that's ridiculous that doesn't make any sense at all. If saving gorillas isn't desirable then the fact that they're highly endangered doesn't mean we should try to save them. In fact if saving gorillas is undesirable we certainly shouldn't try to save them. So that argument makes no sense at all. The negative of that assumption destroyed the argument. And that means that the original statement is an assumption. It is something that needs to be true for the argument to work. We've just seen that if it were false the argument wouldn't work. Okay so that is an assumption. Let's think about the other possibility though. We should try to save all endangered species. Let's look at the negative of that. So we would negate that by saying it's not the case that we should try to save all endangered species. Or more simply we don't have to save all endangered species. Let's put that with the original argument to make a new one. Gorillas are highly endangered. We don't have to save all endangered species but we should try to save gorillas. Now I hope you'll agree that that does make sense. We can maintain that gorillas are highly endangered and we should try to save them without committing ourselves to the view that all endangered species must be saved. So I can perfectly well say yes we don't have to save all of them but we do have to save gorillas. Probably I should carry on and explain why. Why is it that gorillas are special and they need to be saved whereas other animals don't need to be saved. But what I've said here is perfectly consistent. There's no harm in maintaining that gorillas need to be saved but not all endangered species have to be saved. So that argument's okay. That isn't destroyed. It's perfectly reasonable. That means that the original statement wasn't an assumption. It wasn't needed for the argument to work because the assumption can put it. Because the argument can put up with the opposite, the negation. So that's how the negative test works. And remember you negate a statement by putting it's not the case that in front of it which often comes to the same thing as simply inserting a not in the right place. And then the negative of an assumption prevents the conclusion from being drawn. It makes the argument into a nonsense that doesn't work. So you can use this to test any possible assumption to work out whether it's really an assumption, whether it really has to be true for the argument to work. Okay, so let's look at an example from a past critical thinking exam paper. And this example happens to be about David Beckham. Here's the argument. It says that we don't normally have a problem in accepting that people with exceptional intelligence should be well paid. People were happy to significantly reward people with powerful scientific brains when, for example, they win Nobel Prizes. We pay vast amounts for the works of highly talented artists. So why should we complain when geniuses such as David Beckham are also highly paid? It's been calculated that his free kicks demonstrate a staggering mastery of physics. Just before he kicks the ball, he's worked out the factors of kick angle, direction and speed together with degree of spin to get the optimum trajectory. Computers take hours to do what Beckham's brain does in seconds. It's obvious that sporting genius like this should be exceptionally well paid. Okay, now this was actually a multiple choice question. It's asking which of the following is an underlying assumption of this argument. Sporting genius is as rare as any other exceptional intelligence. We should be consistent in the way in which we reward exceptional intelligence. The ability of David Beckham to take free kicks cannot be explained. Society's need for sporting genius is as great as its need for any other exceptional intelligence. And finally, E, sporting geniuses need to work as hard as any other type of genius for their high pay. Okay, at this point you might like to pause the video again and have a think. Which of these do you think is the right answer? Which one of these is an assumption? Okay, well the right answer is B. This is the one that has to be assumed. Let's get clear about why. First of all, B is right because that has to be true for the argument to work. We need to think that we have to be consistent in the way in which we reward exceptional intelligence. Otherwise, the fact that we reward other types of intelligence so highly wouldn't be any sort of reason for thinking that we should pay sporting geniuses really highly. Or let's think of it another way. Let's use the negative test. If we take the negative of this, we don't need to be consistent in the way in which we reward exceptional intelligence. Or it's okay to be inconsistent in the way in which we reward exceptional intelligence. You can see that that destroys the argument. If it's okay to be inconsistent, then it's okay not to pay sporting geniuses lots of money. The fact that we pay other people lots of money wouldn't matter. So B is definitely a right answer. It's not been stated and it needs to be true for the argument to work. The opposite of it, the negative destroys the argument. Let's think about the other options as well and see why they're not right. First of all, A, if we take the negative of that, sporting genius isn't as rare as other exceptional intelligence. Or even sporting genius is more common than other exceptional intelligence. Well, that doesn't destroy the argument. The author of the argument can say, yes, it's more common than other types of intelligence. But what's that got to do with anything? My argument was based on how common intelligence is, how many people there are who are scientific geniuses or sporting geniuses. It was all about fairness. We reward these other people very highly. Sporting geniuses are just as amazing. So to be fair, we should reward them in the same way. Okay, what about C? Well, C isn't assumed. That doesn't need to be true. If we take the negative, the ability of David Beckham to take free kicks can be explained. That doesn't destroy the argument. The author can perfectly well agree that it can be explained, but that doesn't destroy anything. That doesn't have any impact really on this argument about fairness. Okay, if we look at D and take the negative, society's need for sporting genius isn't as great as its need for any other exceptional intelligence. Well, again, that doesn't harm the argument. The argument hasn't got anything to do with how much we need different types of geniuses. It wasn't saying that we should give people like Beckham lots of money because we need them in the same way that we need really good scientists. The argument's based on fairness, not need. So the negative of D doesn't harm it. And finally, E isn't right either. If we say the opposite of that, sporting geniuses don't need to work as hard as any other type of genius for their high pay. Again, that's wrong for similar reasons to before. The argument hasn't got anything to do with how hard these people work. The argument that we should pay people like Beckham really well isn't based on the amount of work they do. It's based on fairness. They're geniuses like these other geniuses, so we should pay them equally highly. Okay, so I hope you can see that B is the right answer here. This is the assumption. It's the thing which hasn't been said but has to be true for the argument to work. Now, you'll want to do a lot of practice with assumptions and look at lots of questions because people often find that they need to think about a few examples in order to kind of get into the groove. And assumptions are so important for the reason that I said at the beginning. Often, the thing that's wrong with somebody's argument isn't what's actually there because typically they thought really hard about that. Typically, what's wrong with somebody's argument is an assumption that they've made, something they haven't thought about that needs to be right, but they haven't thought about it and often it's not right. So it's really important to work out what assumptions people are making in their arguments. One other point before I finish. Not all assumptions are problematic. Sometimes an argument makes an assumption but that assumption is perfectly reasonable. It's probably true and so it doesn't always matter that arguments make assumptions. What matters is when an assumption is made and it's really unclear that it's actually true. So just in this example here with David Beckham, maybe if you agree that we should be consistent in the way we reward exception and intelligence. If you agree with that, then it's not a problem that the argument makes that assumption. It's only a problem for the argument if you think that that assumption is possibly wrong or likely to be wrong. And in fact, you can probably think of some objections to it. Okay, so that's basically the end of this video. So the two things that you need to remember are firstly, assumptions are missing reasons, things that haven't been said. And secondly, they're things that are needed for the argument to work. And there's also this test, the negative test, which can help you to check whether something's assumed. And that says firstly that you negate a statement by putting it's not the case that at the start. And remember that often comes down to just putting a not into the sentence. And secondly, the negative of an assumption destroys an argument. So you can test whether something's assumed by seeing if the negative destroys an argument. Okay, I hope that that's a useful introduction to the idea of assumptions. I hope you'll go away and do lots of practice and really enjoy thinking about them. Thank you very much for watching.