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'

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"On the Mechanical Performance of Logical Inference" — William Stanley Jevons's own account, read before the Royal Society in January 1870, of why the 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 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 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 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.