**Michael Wischmeyer** |

13/08/2006

Valuable Counterbalance to Widespread Misconceptions and Nonsense in Print and on the Internet

Torkel Franzen has created an immensely valuable, deeply fascinating examination of misunderstandings, misconceptions, and outright abuse of Godel's theorems frequently found on the Internet (and occasionally in print). He does so in a cogent, non-confrontational style that makes enjoyable reading. Godel's Theorem - An Incomplete Guide to Its Use and Abuse warrants five stars.

A word of caution is appropriate, however. Chapters 2 and 3 will be heavy going for readers not familiar with formal logic. Although Franzen avoids the details of Godel numbers in his explication of Godel's proof, he does delve into topics like self-referential arithmetical statements, Tarski's theorem, Rosser sentences, weaker variants of the first incompleteness theorem, computably decidable sets, Turing's proof of the undecidable theorem, and the MRDP theorem.

Furthermore, the appendix offers both a formal definition of the concept of a Goldbach-like arithmetical statement and comments on the significance of Rosser's strengthening of Godel's first incompleteness theorem. (Any reader that stays the course with the early chapters will be able to handle the appendix discussions. The short chapter 7 is also more technical as it discusses the completeness of first order logic.)

A word of encouragement is equally appropriate. Chapters 2 and 3 can be browsed, even skipped outright. The later chapters are much more accessible and don't require that the earlier chapters have been mastered; instead, they focus on examples of the misuse of Godel's theorems - from the merely technically inaccurate to the humorously nonsensical. It is these later chapters that makes this book special.

Although words like consistent, inconsistent, complete, incomplete, and system have been carefully defined within the context of formal logic, in normal discourse these words have varied meanings, often leading to vagueness and confusion in discussions of Godel's theorems. Furthermore, Godel's theorems often serve in an inspirational fashion, that is being used as analogies and metaphors in which the essential condition that a system must be capable of formalizing a certain amount of arithmetic is largely ignored.

Invocations of Godel's incompleteness theorems in theology, in physics (like the theory of everything), and in the philosophy of the mind (the Lucas-Penrose arguments) are found in chapters 4, 5, and 6. Chapter 8 addresses the widely publicized philosophical claims of Geoffrey Chaitin on the relationship between incompleteness and complexity, randomness, and infinity.

Godel's Theorem - An Incomplete Guide to Its Use and Abuse may be too much too soon. A reader new to Godel's work might consider starting with Godel's Proof ( The Proof and Paradox of Kurt Godel (by Rebecca Goldstein).