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

TL;DR

This paper reconstructs and executes the original Logic Theorist AI program from 1956 using a new IPL-V interpreter in Common Lisp, successfully proving most theorems from its era, marking a historic reanimation of this foundational AI system.

Contribution

It presents a faithful reimplementation of the Logic Theorist in modern code, enabling its execution and validation after over fifty years.

Findings

Successfully proved 16 of 23 theorems from Principia Mathematica.

First execution of the original Logic Theorist code in over 50 years.

Demonstrates the feasibility of reconstructing historic AI 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.