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Reviewer: Marlin W Thomas

Rereading and reviewing a biography more than 30 years after its first publication subjects the work to the added scrutiny of evaluating it on its own terms and in relation to all that has happened since its first appearance. Not many books can withstand that double scrutiny; this book, however, does. Its division into logical and physical sections, its balancing of intellectual and personal history, its comfortable yet scholarly voice, and its attentiveness to social and historical context are as fresh, engaging, and insightful as they were three decades ago. The biography has not been rendered obsolete by the passage of time; rather, the passage of time reveals how strong of a work it is. The newly written foreword, a model of both breadth and concision, enhances the stature of the work and serves as a summary as well. The book's structure is chronological, but each data point on the time line is an occasion for analysis, historical perspective, intellectual portraiture, and biographical detail. For example, the first chapter situates the Turing family socially between landed gentry and the commercial class, and records Turing's early interest in science. The accumulation and depth of evidence that is brought to bear on that interest, such as reproducing in full a note that includes an organic compound formula, comes close to moving from the thorough to the excessive. The attention to the fullness of detail, however, serves the reader well when the author discusses Turing's work on cryptanalysis during the Second World War. Hodges elegantly weaves personal history with the conceptual background of cryptography and the historical context. His exposition of ciphers and their implementation in the Enigma, the German encoding machine used in the Second World War to transmit messages to, among others, submarine commanders, is a model balance of narrative ease and intellectual rigor. Photographs and diagrams of the Enigma particularize and complement the discussion. Hodges devotes comparable space to the Turing Bombe, the machine he designed to unscramble what the Enigma scrambled. The concern with how mathematical operations-the encoding and decoding of texts-are realized in machines presages the chapter on Turing's proposal for and development of the Colossus, a fully programmable electronic computer that is the physical embodiment of a Turing Machine. Here, as elsewhere, the reader, were it not for organizational cues, could be swamped in the mass of documents and detail presented to illustrate both the technological and administrative obstacles encountered in creating a machine that challenged budgets and mindsets. One of the traditional functions of an intellectual biography is to establish connections between the subject's contributions and the subject's psychology, and all too often those connections are either strained or insufficiently teased out. Hodges steers a middle course that identifies Turing's personality, his achievements, but does overdo that identification. Hodges' exposition of the imitation game-whereby a person has to distinguish between a human and computer based solely on an impersonal, remote interaction with a teletype machine-in terms of Turing's desire to be separate from people and to avoid direct communication with them, illustrates the technique. The author's treatment, especially in the last two chapters, of Turing's homosexuality exemplifies his caution in making biographical facts and social conditions the springboard for grand conclusions. He provides a strong narrative in a dispassionate tone that avoids both lurid detail and retrospective political moralizing. Although there is evidence that Turing participated in his own fall, Hodges does not amplify that evidence to create a sentimental, melodramatic storyline. Although he reaches modest conclusions, such as that Turing's death was a suicide not an accident, he characteristically allows the evidence to speak for itself. This book retains its freshness and relevance more than 30 years after its initial publication, and continues to serve as a model for scientific biography in its balance of the psychological and the technical. The lay reader will come away with a deep understanding of Turing's life and work, and mathematicians and computer scientists will find a stimulating treatment of areas studied by Turing's commanding intelligence. The book has, in sum, universal appeal and a particular excellence. More reviews about this item: Amazon , B&N , Goodreads Online Computing Reviews Service