Joseph Weizenbaum (8 January 1923 – 5 March 2008) was a German-American computer scientist who was born in Berlin, Germany, and died in Ludwigsfelde-Gröben, Germany. Associated with Wayne State University, Harvard University, and the Massachusetts Institute of Technology, where he served as a professor, he is known for ELIZA and his work in computer ethics. He is the namesake of the Weizenbaum Award and the Weizenbaum Institute.

Born in Berlin, Germany, to Jewish parents, he escaped Nazi Germany in January 1936, immigrating with his family to the United States. He started studying mathematics in 1941 at Wayne State University in Detroit, Michigan. In 1942, he interrupted his studies to serve in the U.S. Army Air Corps as a meteorologist, having been turned down for cryptology work because of his "enemy alien" status. After the war, in 1946, he returned to Wayne State, obtaining his B.S. in Mathematics in 1948 and his M.S. in 1950.^[1]

Around 1952, as a research assistant at Wayne, Weizenbaum worked on analog computers and helped create a digital computer. In 1956, he worked for General Electric on ERMA, a computer system that introduced the use of the magnetically encoded fonts imprinted on the bottom border of checks, allowing automated check processing via magnetic ink character recognition (MICR). He published a short paper in Datamation in 1962 entitled "How to Make a Computer Appear Intelligent" that described the strategy used in a Gomoku program that could beat novice players.

In 1963, he took a position of associate professor at MIT on the strength of his SLIP (Symmetric List Processing) software. Within four years, he had been awarded tenure and a full professorship in computer science and engineering (in 1970). In addition to working at MIT, Weizenbaum held academic appointments at Harvard, Stanford, the University of Bremen, and other universities.^[3]

In 1966, he published a comparatively simple program called ELIZA, named after the ingénue in George Bernard Shaw's Pygmalion, which could chat to the user. ELIZA was written in the SLIP programming language of Weizenbaum's own creation. The program applied pattern matching rules to statements to figure out its replies. Driven by a script named DOCTOR, it was capable of engaging humans in a conversation which bore a striking resemblance to one with an empathetic psychologist (programs like this are now called chatbots). Weizenbaum modeled its conversational style after Carl Rogers, who introduced the use of open-ended questions to encourage patients to communicate more effectively with therapists.

He was shocked that his program was taken seriously by many users, who would open their hearts to it. Famously, when he was observing his secretary using the software – who was aware that it was a simulation – she asked Weizenbaum: "would you mind leaving the room please?" Many hailed the program as a forerunner of thinking machines, a misguided interpretation that Weizenbaum's later writing would attempt to correct.^[5,52]

Weizenbaum started to think philosophically about the implications of artificial intelligence and later became one of its leading critics.^[7] In an interview with MIT's The Tech, he elaborated on his fears, expanding them beyond the realm of mere artificial intelligence to explain that his concerns for society and its future were largely because of the computer itself. His belief was that the computer, at its most base level, is a fundamentally conservative force that, despite being a technological innovation, would end up hindering social progress. Weizenbaum used his experience working with Bank of America as justification for this reasoning, stating that computers allowed banks to manage an ever-expanding number of checks in play that would have otherwise forced drastic structural changes, such as decentralization. As such, although the computer made the industry more efficient, it prevented a fundamental overhaul of the system.^[53] Furthermore, Weizenbaum worried about the negative effects computers would have on the military, calling the computer "a child of the military."

When asked about his belief that a computer science professional would more often than not end up working with defense, Weizenbaum detailed his position on the effect of rhetoric, specifically euphemism, on public viewpoints. He believed that the terms "the military" and "defense" did not accurately represent the organizations and their actions. He made it clear that he did not think of himself as a pacifist, believing that there are certainly times where arms are necessary, but by referring to defense as killing people, humanity as a whole would be less inclined to embrace violent reactions so quickly.^[53]

His influential 1976 book Computer Power and Human Reason displays his ambivalence towards computer technology and lays out his case: the possibility of programming computers to perform one task or another that humans also perform (i.e., whether Artificial Intelligence is achievable or not) is irrelevant to the question of whether computers should be put to a given task. Instead, Weizenbaum asserts that the definition of tasks and the selection of criteria for their completion is a creative act that relies on human values, which cannot come from computers.^[51] Weizenbaum makes the crucial distinction between deciding and choosing. Deciding is a computational activity, something that can ultimately be programmed, whereas choice is the product of judgement, not calculation.^[50] In deploying computers to make decisions that humans once made, the agent doing so has made a choice based on their values that will have particular, non-neutral consequences for the subjects who will experience the outcomes of the computerized decisions that the agent has instituted.^[15]

Weizenbaum had five children: one son from his first marriage and four daughters from his second.^[16,8] In 1996, Weizenbaum moved to Berlin and lived in the vicinity of his childhood neighborhood.^[49,11] Weizenbaum was buried at the Weißensee Jewish cemetery in Berlin.^[2] A memorial service was held in Berlin on 18 March 2008.

A German documentary film about Weizenbaum, entitled "Weizenbaum. Rebel at Work.", was released in 2007 and later dubbed into English.^[9] The documentary film Plug & Pray, focusing on Weizenbaum and the ethics of artificial intelligence, was released in 2010.^[10] The interdisciplinary German Internet Institute (Weizenbaum Institute for the Networked Society) was named after Joseph Weizenbaum.^[54]

In 1962, Joseph Weizenbaum published "How to Make a Computer Appear Intelligent" in Datamation, followed in 1966 by "ELIZA — A Computer Program for the Study of Natural Language Communication between Man and Machine" in Communications of the Association for Computing Machinery 9 (pages 36–45). His book Computer Power and Human Reason: From Judgment To Calculation was published by W. H. Freeman in 1976. Weizenbaum also authored several German-language works, including Kurs auf den Eisberg, oder, Nur das Wunder wird uns retten, sagt der Computerexperte (Pendo, 1984), Zur Anpassung des Designs an die digitalen Medien (Form + Zweck, 1997), and Computermacht und Gesellschaft freie Reden (Suhrkamp, 2001). In addition, he wrote the foreword to Rudolf Steiner's Renewal of the Social Organism (Anthroposophic Press, 1985; ISBN 0-88010-126-1 cloth, ISBN 0-88010-125-3 pbk.), and his work Islands in the Cyberstream: Seeking Havens of Reason in a Programmed Society was published in Sacramento by Litwin Books in 2015 (ISBN 978-1-63400-000-0).

External materials concerning Joseph Weizenbaum include his personal archives held at the Massachusetts Institute of Technology and documentation of his recognition as the 1988 winner of CPSR's Norbert Wiener Award for Professional and Social Responsibility. Obituaries following his death appeared in The Independent on 18 March 2008 and in The Times on 24 March 2008, which contains the names of his spouse and children. Further coverage includes an 11 November 2010 Frankfurter Allgemeine Zeitung article about a documentary filmed shortly before his death, as well as Ben Tarnoff's 25 July 2023 article titled "'A certain danger lurks there': how the inventor of the first chatbot turned against AI".