###### English mathematician **Alan Turing** (1912–1954), was a pioneer of computer science and, although he never thought of himself as a philosopher, his 1950 paper, “Computing Machinery and Intelligence,” is one of the most frequently cited in modern philosophical literature. Among his notable accomplishments is also the Turing machine, considered to be the basis of the modern theory of computation.

###### Professor of English at the University of Florida, **David Leavitt** is the author of several books, including “The Man Who Knew Too Much: Alan Turing and the Origins of the Computer.” He is the author of the short story collections Family Dancing (finalist for the PEN/Faulkner Prize and the National Book Critics’ Circle Award), A Place I’ve Never Been, Arkansas, and The Marble Quilt, as well as the novels The Lost Language of Cranes, Equal Affections, While England Sleeps (Finalist for the Los Angeles Times Fiction Prize), The Page Turner, Martin Bauman, or A Sure Thing, and The Body of Jonah Boyd.

###### A recipient of fellowships from the National Endowment for the Arts, the Guggenheim Foundation, and the Institute of Catalan Letters in Barcelona Spain, Professor Leavitt was recently named a Literary Lion by the New York Public Library.

**Q: You’re a critically acclaimed novelist and a professor of English at the University of Florida. What prompted you to write a book on an obscure mathematician by the name of Alan Turing covering such arcane topics as Gödel’s Incompleteness Theorems, recursion theory, Church’s lambda calculus, etc.? Do you have a mathematical background?**

A: My mathematical education ended with high school calculus. Some twenty-five years later James Atlas, esteemed biographer, editor, and founder of Atlas Books, wrote to tell me he was launching a series of short books on great scientific discoveries and to ask me if I might consider contributing a volume on Turing. At that time, I knew something about Turing’s life—in particular, the tragic circumstances of his last years—but virtually nothing about his work. When I agreed to do the book, I assumed that I would soft-pedal the math and focus on Turing’s biography. The more I read, however, the more the math fascinated me. I realized that to do Turing justice I would have to represent how his mind worked and to explore the connections between his forays into mathematical speculation and his strange personal journey.

**Q: Alan Turing is widely considered to be the father of modern computer science. Can you summarize his contributions in this field?**

A. In his famous paper “On Computable Numbers” Turing conceptualizes, for the first time, the idea of a machine capable of calculating any algorithm presented to it. Although the concept of a calculating machine or “difference engine” dates back to the nineteenth century, Turing was the first person to propose—and draw a plan for—a machine that was not task-specific but rather capable of transforming itself into any of an infinite number of task-specific machines: a universal machine. Such a machine, he theorized, would need to be simple in design. More importantly, the “instructions” by which it undertook a specific algorithm would have to be written in the same language as the algorithm itself. In proposing this radical idea, he in effect invented programming and the concept of software. Later in his career, Turing participated in the construction and programming of one of the first supercomputers, the Manchester “Baby.” His last and perhaps most significant contribution to the field was philosophical: in his famous paper “Computing Machinery and Intelligence” he addressed the complex question of whether a machine could ever be said to think and proposed a test to determine the answer.

**Q: As a consequence of his work in the advancement of modern computer science, his research overlapped with philosophy anticipating the concept of artificial intelligence. Can you tell us what his views were on this?**

A: Turing’s argument for computer intelligence rests on the premise that behavior equals identity. If a machine persuades you that it is thinking, then it is thinking. How we behave is who we are. Critics countered that thought necessitated consciousness: to think, a mind or a machine has to be able to know itself to be thinking.

In “Computing Machinery and Intelligence” Turing anticipates not only a future in which thinking machines exist but the likelihood that they in that future will be the victims of discrimination. Fearful of the machines, humans “born in the usual manner” will oppress them. In this regard, his polemic reflects his own experience as a gay man living in a country that criminalized homosexuality. His cry for “fair play for the machines” encodes a cry for an end to discrimination.

**Q: Can you explain Turing’s hypothetical test for whether a computer could think; the so-called Turing Test?**

A: An extremely abbreviated gloss:

C is told that A and B are a man and a woman but not which is the man and which is the woman. C must assign a gender to each purely on the basis of typewritten answers. A and B do everything they can not just to influence C but to suggest that the other is lying. Now let us suppose that A and B are a human being and a machine. C must likewise determine which is which. If the machine persuades C that it can think—that it is human—then it has passed the test. This constitutes, in Turing’s mind, proof that machines can think.

**Q: At Cambridge University, Turing attended lectures by philosopher Ludwig Wittgenstein on the Foundations of Mathematics. The two were said to have argued over certain fundamental issues. Can you tell us more about this?**

A: In his famous seminar on the foundations of mathematics Wittgenstein cast Turing, rather against his will, in the role of the “mathematician.” Their arguments were fruitful and stimulating but, as is usually the case with philosophy, generated more questions than answers.

**Q: It has been said that Turing’s work on deciphering the German Enigma code at Bletchley Park during the Second World War made a significant contribution to winning that war. How so?**

A: As the architect of the “Bombe”—a machine specifically designed to break a code generated by another machine (the German Enigma)—Turing laid the foundations for a massive code-breaking operation as a result of which the Allies were able to gain a significant advantage over the Germans in that portion of the war that took place in the waters of the Atlantic.

**Q: From 1936 to 1938, Turing studied at the Institute for Advanced Studies in Princeton, where Kurt Gödel lectured. Did they cross paths at any point?**

A: Only briefly. Turing was very shy and Gödel, at this point, reclusive.

**Q: How was Turing’s own work related to Kurt Gödel’s Incompleteness Theorem?**

A: David Hilbert called for proofs of the completeness, consistency, and decidability of a mathematical system such as the one put forth by Russell and Whitehead in their tome Principia Mathematica. Godel proved that such a system could be neither complete nor consistent, Turing that it could not be decidable.

**Q: During his final years, Turing became interested in chemistry. Can you describe his work in this area?**

A: This is the aspect of Turing’s life about which I know the very least.

**Q: Turing ended his life after eating a cyanide-laced apple. His death was ruled a suicide, though rumors of assassination still linger. What is your take on this?**

A: So long as the documents and files relating to Turing’s death remain classified, this is an open question.