Kurt Gödel's famous First Incompleteness Theorem shows that for any sufficiently rich theory that contains enough arithmetic, there are some arithmetical truths the theory cannot prove. How is this remarkable result proved? This short book explains. It also discusses Gödel's Second Incompleteness Theorem. Based on lecture notes for a course given in Cambridge for many years, the aim is to make the Theorems available, clearly and accessibly, even to those with a quite limited formal background.

Forever Undecided is the most challenging yet of Raymond Smullyan’s puzzle collections. It is, at the same time, an introduction—ingenious, instructive, entertaining—to Gödel’s famous theorems. With all the wit and charm that have delighted readers of his previous books, Smullyan transports us once again to that magical island where knights always tell the truth and knaves always lie. Here we meet a new and amazing array of characters, visitors to the island, seeking to determine the natives’ identities. Among them: the census-taker McGregor; a philosophical-logician in search of his flighty bird-wife, Oona; and a regiment of Reasoners (timid ones, normal ones, conceited, modest, and peculiar ones) armed with the rules of propositional logic (if X is true, then so is Y). By following the Reasoners through brain-tingling exercises and adventures—including journeys into the “other possible worlds” of Kripke semantics—even the most illogical of us come to understand Gödel’s two great theorems on incompleteness and undecidability, some of their philosophical and mathematical implications, and why we, like Gödel himself, must remain Forever Undecided!

A clear and accessible discussion of the ideas and issues behind chaotic dynamics.

In this fascinating book, mathematician Ed Beltrami takes a close enough look at randomness to make it mysteriously disappear. The results of coin tosses, it turns out, are determined from the start, and only our incomplete knowledge makes them look random. "Random" sequences of numbers are more elusive, but Godels undecidability theorem informs us that we will never know. Those familiar with quantum indeterminacy assert that order is an illusion, and that the world is fundamentally random. Yet randomness is also an illusion. Perhaps order and randomness, like waves and particles, are only two sides of the same (tossed) coin.

What distinguishes laws of nature from ordinary facts? What are the "lawmakers": the facts in virtue of which the laws are laws? How can laws be necessary, yet contingent? Lange provocatively argues that laws are distinguished by their necessity, which is grounded in primitive subjunctive facts, while also providing a non-technical and accessible survey of the field.