Logical Machines (1887)

In the AI Story

The essay's central analytical claim is that mechanical logic machines execute deduction — the one mode of inference whose output is fully determined by its input — without difficulty. "The secret of all reasoning machines is after all very simple," Peirce wrote. "Whatever relation among the objects reasoned about is destined to be the hinge of a ratiocination, that same general relation must be capable of being introduced between certain parts of the machine."

But Peirce was careful to identify what the machines could not do. They could not, he argued, decide which logical operations were worth performing. They could not select premises. They could not evaluate whether the conclusion they derived advanced inquiry or merely extended it mechanically. These were functions of what Peirce called self-control, and he regarded self-control as the mark distinguishing reasoning from mere computation.

The essay remained obscure for most of the twentieth century. It was rediscovered in the 1970s by historians of computing, and its philosophical significance has only become fully apparent in the past decade, as contemporary AI systems have approached — and in some respects surpassed — the operations Peirce analyzed.

The essay's combination of engineering detail (the electrical circuit designs) and philosophical depth (the inferential question) makes it a uniquely prescient document. Peirce was not guessing about the future. He was reasoning about the logical structure of computation in a way that remains valid now that the technology has caught up.

Origin

Written in the aftermath of Peirce's dismissal from Johns Hopkins in 1884 and his retreat to Milford, Pennsylvania, where he lived in increasing isolation.

Marquand had constructed a mechanical logic machine based on an earlier device by William Stanley Jevons. Peirce's 1886 letter proposed that electrical switching could replace Marquand's mechanical apparatus — a proposal Marquand sketched but never built.

Key Ideas

The inferential question. How much of thinking can the machine perform, and what must remain with the living mind?

Mechanization of deduction. Logical relations can be instantiated in physical structures that enforce them automatically.

Self-control as the residuum. What the machine cannot do is evaluate whether its operations are worth performing.

Electrical logic circuits. Peirce's 1886 sketches are recognized as the first known designs for electronic logic gates, predating Shannon by half a century.