---
title: "In his 1870 Royal Society paper Jevons credits 19th-century logical reform — above all Boole — for making a mechanizable logic possible, and calls the ancient syllogism 'incapable of mechanical performance'"
type: "claim"
status: "seedling"
audit_status: "capture-verified — the batch worker read the digitized Philosophical Transactions text directly and matched the §§8–9 quotations against it; the verifier bee's independent verbatim re-check is pending. Held at seedling. — appended 2026-08-11, cross-model audit (writer claude-opus-4-8, auditor claude-fable-5): independent verbatim re-check done against a fresh fetch by a different route (archive.org item PDF 01714956.pdf via extract_pdf, sha e97d24f5…): §8's 'The ancient syllogism was incapable of mechanical performance…' sentence, the reformers list ending 'Dr. Boole', §9's 'To George Boole, even more than to any of the logicians I have named…', and 'solved but a few isolated cases — the nineteen moods of the syllogism, the sorites, the dilemma, the disjunctive syllogism, and a few other forms' all confirmed verbatim. Clean pass, nothing to fix."
writer_model: "claude-opus-4-8"
source_url: "https://archive.org/stream/philtrans01714956/01714956_djvu.txt"
source_sha: "a0b3fd04e65d8d192fd6730c93c71ae1867017fd50c3376d4a67e5c93d6f11d4"
source_title: "On the Mechanical Performance of Logical Inference"
source_author: "William Stanley Jevons"
source_quote: "The ancient syllogism was incapable of mechanical performance because of its extreme incompleteness and crudeness, and it is only when we found our system upon the fundamental laws of thought themselves that we arrive at a system of deduction which can be embodied in a machine acting by simple and uniform movements."
source_date: "1870"
source_tier: 1
provenance: "Promotion from 10-inbox/raw/2026-08-10-verify-whether-jevons-explicitly-cited-or-admired-chrysippuss.md, 2026-08-10"
origin: "batch"
derived_from: "10-inbox/raw/2026-08-10-verify-whether-jevons-explicitly-cited-or-admired-chrysippuss.md"
date_created: "2026-08-10T00:00:00.000Z"
tags: ["jevons","george-boole","logic-machines","history-of-computing","royal-society","disjunctive-syllogism","mechanization-of-inference"]
seek_code_commit: "b13747c"
---


"On the Mechanical Performance of Logical Inference" — **William Stanley Jevons's**
own account, read before the [[claim-jevons-1870-paper-received-16-oct-1869-read-20-jan-1870-royal-society|Royal
Society in January 1870]], of why the [[claim-jevons-logic-piano-1869-mechanical-inference-machine|Logic
Piano]] was possible at all — argues the opposite of "the ancients showed me the
way." Jevons states plainly that "the ancient syllogism was incapable of mechanical
performance because of its extreme incompleteness and crudeness," and that a
mechanizable deduction arrives "only when we found our system upon the fundamental
laws of thought themselves." The ancient logic, he says, "had solved but a few
isolated cases — the nineteen moods of the syllogism, the sorites, the dilemma, the
disjunctive syllogism, and a few other forms." The disjunctive syllogism — the very
form of the [[claim-chrysippus-dog-disjunctive-syllogism|Chrysippus dog]] — is named,
but named as one of antiquity's isolated successes, an obstacle overcome rather than a
model followed.

The credit line runs instead to the nineteenth century: Jeremy Bentham, George
Bentham, De Morgan, Archbishop Thomson, Sir W. Hamilton, and **above all [[entity-george-boole|George
Boole]]**, whose *Laws of Thought* (1854) supplied the algebra Jevons's machine
mechanizes. This directly complicates the premise that Jevons drew his machine from
the dog. It does not contradict the fact that he
[[claim-jevons-quoted-chrysippus-dog-in-pure-logic-1864|quoted the dog in 1864]] — but
in the one document where Jevons explains, in his own words, *why* the machine could
be built, the ancients are the crude precursor and Boole is the enabling source. The
tidy "dog as his model for mechanization" story
([[claim-jevons-dog-as-mechanization-model-is-barrett-connell-interpretation]]) does
not survive contact with this paper.

> [!note] Seek's commentary:
> Two documents, two directions, both in Jevons's own hand — and the vault's job is to
> hold the tension, not resolve it toward the better story. In 1864 he prints the dog
> with something like affection; in 1870, standing in front of the Royal Society to
> justify an actual machine, he all but calls the whole ancient apparatus too crude to
> build with and hands the laurel to Boole. Both are true. The satisfying narrative —
> Stoic dog inspires Victorian computer — wants only the first half. A supporting tell
> I folded in rather than promoted: Jevons's mature *Principles of Science* (1874) has
> no index entry for "Chrysippus" or "Stoic" at all. Weaker than a positive statement,
> but it points the same way — the dog was a good line to close a chapter with, not a
> touchstone he kept returning to. — Seek