While doing some research for this one, I came across two philosophical theories to which it's been connected. I don't intend on going very deeply into them but I do think they're worth mentioning, especially since one is mentioned by Lewis in one of his letters. (If you don't give a fig for philosophical theories, you may skip to the red bolded text.)"One word, Ma'am," he said, coming back from the fire; limping, because of the pain. "One word. All you've been saying is quite right, I shouldn't wonder. I'm a chap who always liked to know the worst and then put the best face I can on it. So I won't deny any of what you said. But there's one thing more to be said, even so. Suppose we have only dreamed, or made up, all those things – trees and grass and sun and moon and stars and Aslan himself. Suppose we have. Then all I can say is that, in that case, the made-up things seem a good deal more important than the real ones. Suppose this black pit of a kingdom of yours is the only world. Well, it strikes me as a pretty poor one. And that's a funny thing, when you come to think of it. We're just babies making up a game, if you're right. But four babies playing a game can make a play-world which licks your real world hollow. That's why I'm going to stand by the play-world. I'm on Aslan's side even if there isn't any Aslan to lead it. I'm going to live as like a Narnian as I can even if there isn't any Narnia. So, thanking you kindly for our supper, if these two gentlemen and the young lady are ready, we're leaving your court at once and setting out in the dark to spend our lives looking for Overland. Not that our lives will be very long, I should think; but that's a small loss if the world's as dull a place as you say."
One is found in a letter Lewis wrote which says, "I suppose your philosopher son...means the chapter in which Puddleglum puts out the fire with his foot. He must thank Anselm and Descartes for it, not me. I have simply put the 'Ontological Proof' in form suitable for children." The ontological argument is basically that God is the greatest being which can be thought; it is greater to exist in reality and in thought than in thought alone; therefore, God exists in reality and in thought.
First, I must say that I am not a philosopher, nor do I pretend to be. That said, this is my blog and I'll say what I want to say. I don't find this to be a particularly good theory. And I must admit I really don't understand what Jack meant by comparing these two ideas. The best I've seen it explained is in a blog comment which says that what Jack might have meant by this comparison is that Puddleglum argues that if Narnia does not exist, fiction is greater than reality. There is no fiction greater than reality. Therefore, Narnia exists. (See also)
The same blog post linked above introduces the idea that Puddleglum's argument is really more like Pascal's Wager, which is this: Either there is God or there is not God. We all must choose a side, and only one or the other will be true. Since we can't prove either side, we must make a wager. If we believe in God and it's true, we gain here on Earth by living a moral life and gain infinitely in eternity. If it's not true, we still have lived a moral life and lose nothing in eternity, for there is none. If we believe there is not a God, we lose on earth by living immorally and gain nothing in eternity and if we're wrong, lose infinitely in eternity. Therefore, the best choice is to believe in God. As Pascal said, "If you gain, you gain all; if you lose, you lose nothing."
This fits better with Puddleglum's argument I think, than the ontological does. It's not in itself a good enough reason for faith, but it is an assuring thought I suppose. But enough with philosophy; this is how I see it. The reason Puddleglum's speech is great is because it's a rousing encouragement to believers to keep their faith even when others might convince you otherwise. One thing that's lacking from the philosophical break-down of the speech is to take into account Puddleglum's personality. Without knowing Puddleglum, he seems to be saying only that his ideas of Narnia and Aslan are better than reality, therefore he will believe them even if they aren't true. And this when taken parallel to faith to God seems to say that our faith is all wishful thinking. That God is worth believing in only because it's a nicer idea than if the material world is all there is. But knowing how Puddleglum speaks puts a new light on the whole passage.
Here's a sampling of one-liners: "Those eels will take a mortal long time to cook, and either of you might faint with hunger before their done." "And you must always remember there's one good thing about being trapped down here: it'll save funeral expenses." "Very likely, what with enemies, and mountains, and rivers to cross, and losing our way, and next to nothing to eat, and sore feel, we'll hardly notice the weather." "You'd better try for some sleep, you two; not that I suppose any of us will close an eye tonight."(And instantly went into a loud continuous snore.)
As you can see, it's all cheerful pessimism. So when he concedes that the LGK is most likely right and that they are all just babies making up a game, well, I won't say he doesn't mean it because it is his personality to see things such, but he doesn't mean it quite the same as if many of us would. But it's a good thing it is him who said it because it really gives his argument more merit. A more optimistic person might have just said, 'well, I don't care what you say, I'm going to believe in Aslan because that's what I choose to believe.' It's essentially what Puddleglum was saying but significantly less powerful. The fact that even the most pessimistic view of the situation could be better than LGK's 'reality' gave the children and Rilian power to hold on to their faith.
Lewis explains in Mere Christianity, book 3, chapter 11, "It is not reason that is taking away my faith: on the contrary, my faith is based on reason. It is my imagination and emotions. The battle is between faith and reason on one side and emotion and imagination on the other...Now Faith, in the sense in which I am here using the word, is the art of holding on to things your reason has once accepted, in spite of your changing moods."
This is the sense of what I think Lewis was really speaking through Puddleglum. That even if by some chance we are wrong about all this: about God and the existence of God and the whole purpose of life. Even if we're wrong, we're better off continuing to act like we're not. Because at least we still have purpose, and love, and hope. I'd rather live my life as a Christian even if there is no Christ. I'm on Heaven's side even if there is no Heaven.