Now we've learned how to identify an argument and put it in standard form. We've also learned from the definition of argument, that the premises are intended to be reasons for the conclusion. Great. Intended to be a reason for the conclusion. Well intentions are nice, but success is better. What we need to figure out is when the person succeeds in giving premises that really are reasons for the conclusion. For simplicity, let's focus on argument whose purpose is justification. Then the question is, do the premises justify you in believing the conclusion? Well, imagine that you don't know whether there's any life on Mars. You have no evidence one way or the other. Then you ask a friend and the friend says ha, I know there's life on Mars. I can prove it to you. Here, this argument will show you that there's life on Mars. There is at least one bacterium on Mars. Therefore there is life on Mars. Now notice that if the premise is true the conclusion has got to be true. And if you and your friend are justified in believing the premise then you and you are friend are also justified in believing the conclusion. So this argument looks pretty good so far but of course you have to ask your friend, well how do you know that there's at least one bacterium on Mars? And suppose your friend says, well I'm just guessing. Then the argument is clearly no good. If there's no reason to believe the premise because your friend is just guessing then you're not justified in believing that premise. And if you're not justified in believing the premise then how can that premise make you justified in believing the conclusion. More generally an argument cannot justify you in believing the conclusion unless you are justified in accepting the premises of that argument. Now, suppose your friends says oh, but I do have a reason for the premise I do then we have to ask what kind of reason is it? And, at that point your friend needs to express reason. And, how do we express reasons? In arguments. So, your friend has to give another argument for the premise. Where the premise of the first argument is the conclusion of the second argument. Wait a minute, we got a problem. Because that second argument is itself going to have premises. And you have to be justified in believing those. So the premises of the second argument have to be the conclusion of a third argument. And so on and so on because the third argument needs premises. They have to be justified. So they have to be the conclusion of another argument. Which also has to have premises. And those have to be the conclusion of another argument. And so on and so on. It looks like we've got a real problem here. In order for the premises to be justified they have to be backed up by an argument, but the argument has premises of its own that have to be backed up by another argument and so on, and so on. This problem is called the problem of the skeptical regress because you regress back to one argument after another, after another, after another, after another, after another, after another. And it's hard to see how that regress, is ever, going to come to an end. There seem to be only three ways to get around this skeptical regress. The first is to start with a premise that's unjustified. If it's unjustified, then it doesn't need an argument to back it up. And that means that you're not going to have this chain of arguments going back and back and back and back and back and back and back. The second possibility is to have a structure where the arguments move in a circle. One claim is justified by another which is justified by another which is justified by another which is justified by the first claim. And they just move in a circle. The third possibility, is that the chain of arguments goes back infinitely. It never stops. Every claim has an argument to back it up. And there's no end, so you never have a prentice which doesn't have an argue to back it up, because it's infinite. Those seem to be the three main options here to avoid the skeptical regress. The first possibility then, is to start with a premise that's unjustified. And that seems pretty neat if you can get away with it but we already saw why that won't work. We saw your friend arguing that there's life on Mars because there's at least one bacterium on Mars, and he was just guessing. If you just guess at your premises, you have no reason to believe them. Then, an argument that uses those premises cannot justify you in believing the conclusion. But in addition, just think about it this way. You could prove anything if we let you start with unjustified premises. If you can just make up your premises for no reason then there's no stopping you from believing whatever, including things that are obviously false. So it seems to be a real problem to start with premises that are unjustified. Next, the second way to respond to the skeptical regress is to use a circular structure. and it's kind of neat, if you think about it, because, if you want to prove one claim, you prove it on the basis of another claim. And then you prove that second claim on the basis of the third, and the third on the basis of the fourth and the fourth on the fifth, and the fifth on the basis of the first. And now you've got this circle, and the arguments go in a circle. But that means that every premise has an argument to back it up. Cause you can keep going around the circle forever. You can think about it a little bit, it'll be obvious that that's no good. And that can be shown by looking at the smallest circle there is. So suppose your friend says, I can prove there's life on Mars. Here's my argument. There's life on Mars, therefore there's life on Mars. Clearly, that's no good. And the reason why it's no good is that if he didn't know whether there was life on Mars to begin with, you wouldn't know whether the premise was true. because if you don't know the conclusion you can't know the premise, since the premise is the conclusion. So if you're not justified in believing the conclusion to begin with, you're not justified in believing the premise. And that means that the argument didn't really get you anywhere. It just ends up where it started. And in addition, it has the same problem we saw in the first approach involving unjustified premises. Because you can use circular arguments to prove anything. You can prove there's life on Mars there's life on Mars therefore there's life on Mars. You can prove there's no life on Mars therefore there's no life on Mars. You can do it either way and the fact that an argument can be used either way to prove either conclusion suggests there's a big problem with that kind of argument. So now we are down to the third and final way to get around the skeptical regress, and that is to use an infinite chain of arguments. If you think about it, in a concrete case, you'll see why that's a problem as well. Suppose your friend says there's life on Mars and I can prove it. And you say fine, give me a reason? Well there's a least one bacterium on Mars, therefore there's life on Mars. And you go okay, fine but how do you know there's a least one bacterium on Mars? I've got another argument he says, there are at least two bacterium on Mars, therefore there's at least one bacterium on Mars. But how do you know there's at least two? Well, there are at least three bacteria on Mars. Therefore, there are at least two bacteria on Mars. But how do you know there are at least three? Well, there are at least four so there are at least three. Well, there are at least five so there are at least four. Well, there are at least six so there are at least five. And so on and so on and so on. You could go on infinitely. So an infinite chain of arguments. Would allow you to prove that there's life on Mars even if you have no evidence whatsoever of any bacteria because you're going to have an argument but if the premise that you are arguing from doesn't have an independent justification then the infinite chain is going to be no good at all in justifying the conclusion of that argument. So many people see this skeptical regress as a deep and serious philosophical issue. If the unjustified premise approach doesn't work, and the circular argument structure doesn't work, and the infinite chain of arguments doesn't work, then it's hard to see how we can get around the problem. Which is to say, it's hard to see how any kind of argument could ever justify us in believing anything. Philosophers really scratched their heads about that for a long time. And worry about it. It keeps them up at night. But we're going to have look at how practical people solve a similar problem in everyday life. So how we solve this skeptical regress problem in everyday life well there various tricks which you can use. For example, one way is to just start from assumptions that everybody shares. So if I say, well you really ought to buy a Honda because Hondas are very reliable cars. Then I'm assuming that you want your car to be reliable. You don't like to have to take it in to the mechanic all the time. You don't want it to break down on the road. And if you want reliability and I want reliability, then we can start from the assumption that reliability's a good thing and that that's a reason to buy a car that is reliable. But of course you might say, well but our Honda's reliable. And then I might. Appeal to an authority. Well, it's obvious that they are. Or, Consumer Reports has done a study that shows that they're reliable. And I can appeal to an authority, and if you accept that authority, go, Consumer Reports, we can trust them, then, my argument's going to work. You're going to have a reason to believe the conclusion, and it might persuade you, and make you come to believe the conclusion. But, suppose that someone is going to raise an objection. They say, well, Consumer Reports has been wrong before. They might be wrong this time. Well, then, I need to discount that objection. I need to respond to it, and say, well, maybe they have been wrong sometimes, but this time, you know, they've got a good study and it was careful, or whatever. And the but means, I'm discounting the objection that you have raised, and I might even discount it in advance. Well I might just guard my client I might say, well. They might be right, in this case. Or they're probably right, without claiming that they definitely are right. So I can assure you by signing as some kind of authority. I can discount objections and I can guard my premises by saying, well it's probably right. Instead of saying that it's definitely right. And those are three ways of solving. The skeptical regress problem in everyday life that we're going to look at in much more detail in the next three lectures. But the point of this lecture has been more general. In order to solve the skeptical regress problem, you have to find some assumptions that you and your audience share. They might be assumptions about the premises of your arguments. They might be assumptions about authorities that supposedly support your premises and that they accept as authorities or whatever. But there have to be some assumptions that you share with your audience in order to get the argument going. And that's kind of tricky because it's going to depend on the context. If you are dealing with an audience that shares a lot of your assumptions that argument is going to be relatively easy. But if you are dealing with an audience that doesn't share any of your assumptions it's going to be impossible. And, in areas where there's a lot of disagreement it's going to be hard to get your argument going because your premises are going to be questioned and denied or rejected by the people in the audience. So, what these tricks do, is they give you ways to get the argument going. But they're not going to work in every case. And we'll have to look at that, as we're looking at these three different ways to solve the skeptical regress problem in the next three lectures.