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What was ELIZA?
Weizenbaum introduced ELIZA in “ELIZA—a computer program for the study of natural language communication between man and machine,” published in Communications of the ACM, volume 9, number 1, pages 36–45, in January 1966. He described its scope directly: “ELIZA is a program which makes natural language conversation with a computer possible.”
The original ran within MIT’s MAC time-sharing system. It was written in MAD-SLIP for an IBM 7094. ELIZA is commonly called one of the first chatbots, but that later label can obscure the paper’s focus: demonstrating a way to produce certain forms of computer conversation and examining the procedures behind it.
How did ELIZA work?
ELIZA did not interpret a sentence as a person would. It searched a user’s input for keywords, used a matching rule to break the text into parts, and applied a corresponding rule to assemble a reply. Weizenbaum’s paper calls these “decomposition rules which are triggered by key words appearing in the input text” and “reassembly rules associated with selected decomposition rules.”
The program’s operation depended on five problems Weizenbaum identified:
- Identify keywords: Find terms in the input that can trigger a response.
- Find minimal context: Select the relevant parts of the input around a keyword.
- Choose transformations: Decide how to rearrange or transform those parts.
- Handle inputs with no keywords: Provide a reply when no scripted keyword applies.
- End the exchange: Give the script a way to conclude a conversation.
The rules could make a reply feel connected to what the user had said, even though the connection came from pattern matching and rearrangement rather than demonstrated comprehension.
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What was the DOCTOR script?
ELIZA was the program framework; DOCTOR was a script that shaped one kind of conversation. It used therapist-like prompts to reflect a person’s wording, invite elaboration, or turn a statement into a question. In the paper’s example, the user says, “Men are all alike.” ELIZA replies, “IN WHAT WAY?”
Weizenbaum made an important distinction between the program and its conversation rules: “An important property of ELIZA is that a script is data; i.e., it is not part of the program itself.” Because a script was separate data, the same framework could support different conversational patterns, including scripts in different languages.
Was ELIZA really a therapist?
No. DOCTOR simulated some features of a psychotherapy conversation; it was not evidence that ELIZA understood a person’s circumstances, provided clinical care, or could replace a therapist. Its therapist-like style illustrates how reflecting a user’s own words and asking open-ended questions can create an impression of attention without establishing understanding.
What survives in the historical record?
MIT Distinctive Collections catalogs “Computer conversations, 1965” as a complete printout of ELIZA source code in MAD-SLIP, with the DOCTOR script attached. The record establishes an archival source for the original program, distinct from later ports and reconstructions.
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In a 2025 preprint, Rupert Lane, Anthony Hay, Arthur Schwarz, David M. Berry, and Jeff Shrager describe restoring ELIZA on CTSS running on an emulated IBM 7094. They report that the archive includes an early DOCTOR script, nearly complete MAD-SLIP code, and supporting MAD and FAP routines. Those restoration details are the authors’ account, not a claim about the original program’s present-day operation.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How should ELIZA’s legacy be understood?
Later accounts often frame ELIZA as the invention of a chatbot. A 2024 preprint by Jeff Shrager instead argues that Weizenbaum developed it as a research platform for human-machine conversation and interpretation, not with the aim of inventing a chatbot. That is a scholarly interpretation; the 1966 paper itself describes enabling certain forms of conversation and exposing how the program produces them.
The famous story that a secretary asked Weizenbaum to leave the room while she spoke with ELIZA should also be treated cautiously. A 2026 Weizenbaum Institute publication says the secretary has not been located and that accounts of the anecdote vary. The story may capture the impression the program made, but it is not a verified user-response statistic or settled proof of what happened.
ELIZA’s significance lies in the contrast it makes visible: a fixed set of text patterns can sustain a convincing conversational rhythm, especially when it echoes the user, without showing that the system understands the exchange.
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