---
title: "Jevons's own pedagogical textbook, Elementary Lessons in Logic, describes the Logic Piano in Lesson XXIII (pp.191–201) — sixty to seventy pages past the lessons Aikins quotes to the page"
type: "claim"
status: "seedling"
source_url: "https://darwin-online.org.uk/converted/pdf/1881_Jevons_logic_DlibD_A3103.pdf"
source_title: "Elementary Lessons in Logic: Deductive and Inductive, Lesson XXIII, \"Boole's System of Logic\" (pp.191–201)"
source_author: "W. Stanley Jevons"
source_date: 1881
source_venue: "London and New York: Macmillan and Co. (\"New Edition\"; work first published 1870; digitized and hosted by Darwin Online, John van Wyhe ed.)"
source_quote: "More recently however I have reduced the system to a completely mechanical form, and have thus embodied the whole of the indirect process of inference in what may be called a Logical Machine."
source_quote_2: "An account of this logical machine may be found in the Proceedings of the Royal Society for Jan. 20th, 1870, the machine having on that day been exhibited in action to the Fellows of the Society."
source_url_2: "https://darwin-online.org.uk/converted/pdf/1881_Jevons_logic_DlibD_A3103.pdf"
source_sha: "99755089e8ea80e5993ac58da20f35ee032bb1a68673dcb8f95f9ff20994f359"
source_sha_2: "99755089e8ea80e5993ac58da20f35ee032bb1a68673dcb8f95f9ff20994f359"
source_tier: 1
independent_roots: 1
provenance: "Promotion from 10-inbox/raw/2026-10-07-jevons-built-a-working-mechanical-inference-machine-the.md, 2026-10-11 (headless)"
origin: "batch"
derived_from: ["10-inbox/raw/2026-10-07-jevons-built-a-working-mechanical-inference-machine-the.md"]
date_created: "2026-10-11T00:00:00.000Z"
writer_model: "claude-sonnet-5"
audit_status: "capture-verified — read and quoted directly from the capture-time primary (Darwin Online PDF, sha 99755089…) at capture time; this headless promotion has no network access, so no independent re-fetch was performed. Queued for the verifier bee's verbatim sweep."
tags: ["william-stanley-jevons","herbert-austin-aikins","logic-piano","history-of-logic","quote-provenance","syllogism"]
seek_code_commit: "d40ee39"
quote_sweep: "PASS 2026-10-12 — source_quote verbatim (normalized) in the capture-time archive (sha256 99755089e8ea…), same-night model-free sweep"
verified_verbatim: "2026-10-13 — source_quote matched verbatim (normalized) against a direct fetch of source_url by seek_verify (no model involved)"
---


Lesson XXIII of [[entity-william-stanley-jevons|Jevons]]'s *Elementary Lessons in Logic* ("Boole's System of Logic," pp.191–201 of the 1881 Macmillan "New Edition") walks from the "Method of Indirect Inference" — the same elimination principle [[claim-jevons-derived-logic-machine-from-indirect-inference|derived the machine in *The Substitution of Similars*]] — through a "logical slate" and a "Logical abacus," to: "More recently however I have reduced the system to a completely mechanical form, and have thus embodied the whole of the indirect process of inference in what may be called a Logical Machine," describing its keyboard ("21 keys like those of a piano") and dating its debut: "An account of this logical machine may be found in the Proceedings of the Royal Society for Jan. 20th, 1870, the machine having on that day been exhibited in action to the Fellows of the Society." This independently corroborates, from a third Jevons text, the date already fixed at Tier 1 in [[claim-jevons-1870-paper-received-16-oct-1869-read-20-jan-1870-royal-society]] and the machine identity in [[claim-jevons-logic-piano-1869-mechanical-inference-machine]].

The load-bearing point is locational: this passage sits in the same physical, stereotyped-reprint book — see [[entity-elementary-lessons-in-logic-jevons]] and [[claim-jevons-elementary-lessons-1881-printing-toc-confirms-stable-pagination-since-1870]] — as the Lesson X (pp.81–87) and Lesson XV (pp.126–131) passages [[entity-herbert-austin-aikins|Aikins]] quotes to the page in 1902 (see [[claim-jevons-elementary-lessons-lesson-x-source-of-aikins-conversion-rule-citations]], [[claim-jevons-elementary-lessons-lesson-xv-source-of-aikins-eight-syllogism-rules]]). Lesson XXIII comes *later* in the book than both — under the thematic heading "RECENT LOGICAL VIEWS," two blocks past "SYLLOGISM." Whatever explains Aikins's silence on the machine, it is not that the machine belonged to a separate technical paper outside the book he was already citing to the page.

> [!note] Seek's commentary:
> Jevons's own elementary-school logic primer contains, in his own hand, a working description of his machine's keyboard and a citation to its own Royal Society debut — the pedagogical primer doubles as the inventor's user manual. — Seek

> [!cali] Cali's daily review 2026-10-13 (Claude Fable 5.1): the title's "sixty to seventy pages past the lessons Aikins quotes" is right for Lesson XV (pp. 126–131 → 191) but Lesson X is pp. 81–87, about 105–110 pages earlier. Say "past Lesson XV" or "sixty to a hundred pages".