Executable Archaeology: Reanimating the Logic Theorist from its IPL-V Source

2026-03-13

AI Summary

This study presents a faithful reproduction of the 1956 Logic Theorist—the first artificial intelligence program—by implementing an original IPL-V interpreter in Common Lisp, based on Stefferud’s 1963 transcription. This effort resolves a longstanding historical challenge: the inability to execute the program for over half a century. For the first time since its inception, the Logic Theorist has been successfully run, enabling executable archaeology of AI’s foundational system. Under the original search constraints, the reproduced system proved 16 of the 23 theorems from Chapter 2 of *Principia Mathematica*, matching documented historical results. These findings confirm the program’s authentic reasoning capabilities and behavior, establishing a verifiable computational replication that offers a rigorous empirical basis for studying early AI research.

Technology Category

• Knowledge Representation and Reasoning: Logic Programming
• Cognitive Modeling & Cognitive Systems: Conceptual Inference and Reasoning
• Constraint Satisfaction and Optimization: Satisfiability Modulo Theories

Application Category

• Search and Retrieval-Augmented AI: Large language models for search
• Semantics and Knowledge: Data modeling to support human-machine intelligence, including LLMs agents, intelligent system behavior, explanations, and user-friendly interactions
• Economics, Online Markets and Human Computation: Cost models of using LLMs in production systems

Abstract

The Logic Theorist (LT), created by Allen Newell, J. C. Shaw, and Herbert Simon in 1955-1956, is widely regarded as the first artificial intelligence program. While the original conceptual model was described in 1956, it underwent several iterations as the underlying Information Processing Language (IPL) evolved. Here I describe the construction of a new IPL-V interpreter, written in Common Lisp, and the faithful reanimation of the Logic Theorist from code transcribed directly from Stefferud's 1963 RAND technical report. Stefferud's version represents a pedagogical re-coding of the original heuristic logic into the standardized IPL-V. The reanimated LT successfully proves 16 of 23 attempted theorems from Chapter 2 of Principia Mathematica, results that are historically consistent with the original system's behavior within its search limits. To the author's knowledge, this is the first successful execution of the original Logic Theorist code in over half a century.

Problem

• Logic Theorist
• IPL-V
• executable archaeology
• artificial intelligence history
• program reanimation

Innovation

• Executable Archaeology
• Logic Theorist
• IPL-V
• AI History
• Common Lisp