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So it looks like if we want to answer scepticism, we might need to do so in a slightly different way,

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looking for a straightforward argument to justify this that justify knowledge against the sceptic looks intrinsically rather problematic.

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Now, Gillmore, a very famous Cambridge philosopher of the early 20th century.

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He suggested the following refutation of scepticism.

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Here's one hand. Here's another hand.

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Well, if this is a hand. If this is the hand, then there's an external world because hands a physical object.

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Therefore, there is an external world and scepticism is refuted.

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No one's first reaction on coming across that argument is to think this is just ridiculous.

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Come on. I wanted a serious argument against the sceptic. And all this chap saying is he has one hand.

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Here's another. There you are. Hands exist. External objects exist.

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Surely that isn't any good. Well, I think one can look a little bit deeper into this and see that there may be a potentially valuable strategy here.

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Now, two very well-known forms of argument are dignified with ancient Latin names,

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you will quite likely have come across at least the first of these very commonly used modus opponent's modus

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pronouns is the method of inference whereby you go from P implies Q and P is true to the conclusion that Q is true.

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That is clearly a valid method. The inference if P does imply Q that just means that if P is true cuz through two.

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So if he is true, it follows that Q is true. But notice that there is another valid form of inference which is also connected with implication.

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And it's called modus tolland. P implies Q Q is false, therefore P is false.

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Think about it for a moment. Cheque. You agree that is a valid form of inference.

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If P implies Q that means if he's true. Q has to be as well.

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So if Q is false, P can't be true. So unlike the other two methods of inference, you can't say P implies Q.

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Q therefore p that's invalid and it's invalid to say P implies Q not p therefore not.

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Q But these two are both above reproach.

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Now what that means is that if you have an implication, P implies.

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Q You can't only argue forwards, you can also, as it were, argue backwards.

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So let me give you a practical example of this. If you look in the Bible in Chapter 20 of Deuteronomy,

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you will find that the Jews are supposedly commanded to annihilate six whole

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nations of people who have the misfortune to live in the cities that the Lord,

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your God has given you for an inheritance and you're told to save alive nothing that breathes but utterly destroy them,

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not only the fighting men, but the women, children, animals, everything.

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Now you can imagine a religious fundamentalists who argues like this.

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Everything in the Bible is true. Therefore, Genesis genocide is sometimes desirable.

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But you can imagine a philosopher arguing in the opposite way. Genocide is never desirable.

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Therefore, not everything in the Bible is true. Now, the point here, what this highlights is this.

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The two people who argue in these ways are obviously disagreeing, but we can focus that disagreement on the two underlined premises.

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They can agree about what the Bible says. One of them is starting from the premise that everything in the Bible is true.

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One of them is starting from the premise that genocide is never desirable. And you can ask yourself, well, which of those two do I hold more strongly?

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And I think most people would say the latter has a lot more to commend it than the former.

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And this is the sort of thing that could give pause to somebody who starts off from the premise that everything is in the Bible is true.

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So what I'm pointing out here is the fact that when we consider philosophical problems, we don't always start from given premises and argue forwards.

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Sometimes we look at where those premises lead us and then rethink our commitment to those premises.

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So I can imagine lots of Christians might very well start from the hypothesis that everything in the Bible is true.

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Baby, they taught it when they're young and so on.

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Then when they come across these things, they don't just argue forward and say, yeah, okay, this follows.

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They actually go back and reconsider the premises from which they start.

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Now, let's take a look at Moore's argument in that light.

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If this is a hand, there is an external world. Okay.

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Because if this is a hand, it's an external object and a physical object, and therefore there is an external world.

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So that's agreed. And more is effectively, effectively saying, we know this is a hand.

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Therefore, we know there's an external world. Whereas the sceptic says we don't know that there's external world.

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Therefore, we don't know that this is a hand. Think of that in the light of one person's modus pronouns, one person wants to argue forward.

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One person wants to argue backwards.

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More can perhaps plausibly claim that his premise we know this is a hand is more plausible than the premise of the sceptic.

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We don't know that there's an external world that, after all, is a very difficult theoretical claim.

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The claim that we do not know that there's an external world.

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The claim that we know this is a hand might seem when you put the two against each other to have more to commend it.

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So in effect, what Moore is saying is that Descartes is wrong to put all the onus of proof on the person who wants to oppose the sceptic.

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The sceptic, too, is making a substantial claim, a substantial claim that we do not know certain things.

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Maybe that needs to be put against the claim of ordinary believers that they do no such things.

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OK, well, probably most of us would like to agree with more.

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We'd like to think. Yes, we do know that this is a hand. But the argument still seems rather crude.

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It looks as though we want some sort of philosophical argument rather than just a bare common sense claim to justify knowing that this is a hand.

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But as I've said, the Cartesian arguments take arts arguments have great difficulty doing the job.

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They seem to be trying to pull themselves up by their bootstraps.

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As I've said, if you try to justify your faculties using your faculties, it just looks circular.

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So trying to get anything more substantial than Moore's argument does seem rather thin or can do, certainly from many perspectives.

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It seems hard if we rely on the sort of strategy that Descartes tries.

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So many recent philosophers have moved away from the Cartesian idea.

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That is the idea of trying to argue from the inside, trying to prove everything,

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using our faculties and what is immediately apparent to us towards a position called externalism.

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And we'll be discussing that next time. If you've covered induction at all and looked at Mellors approach to induction, I mentioned it last time.

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Very briefly, you'll see that there's a close similarity there as well.

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Externalism has become a very popular way of addressing the sceptic.

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Okay, so I'm putting that on one side till we come back to knowledge.