(a classic from my heydays on IIDB, 6 years ago)
One day in heaven, the philosopher was walking with God, waxing philosophical.
God: Everything you ever wanted is here.
Philosopher: Everything? Do you mean the Truth, too?
God: Why, yes. If its true, its in the Book of the Truth.
Philosopher: What’s that?
God: Come follow me.
They walk towards the Official Library of Heaven, where all the books that have ever existed, or will exist, are located. In the center there’s a tall podium with the biggest book ever lying atop of it, and open. The golden letters are printed in type 6 font, new roman times style, on the finest paper.
God: Every single truth is in this book.
Philosopher: Indeed? All true sentences?
God: But of course. I am essentially omniscient and I also know this to be true. That’s also in there!
Philosopher: Au contraire, mon deux.
Philosopher: I can think of at least one true sentence that cannot be in there.
God: Surely thou jest!
Philosopher: Not at all, your eminence.
God: Alright, what is this sentence? I warn you it cannot be meaningless. I am wise to the art of sophistry!
The philosopher takes a piece of a paper and writes “This statement is not in the Book of Truth.” God’s eyes bulge, and He begins to stammer.
Philosopher: Is this sentence in there? If so the book contains a falsehood. If not, then the book does not have all true sentences. Therefore it is not the Book of Truth.
God: Oh, dear. I hadn’t thought of that. I should have never made that Cretean….