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Peirce, "The Nature of Meaning" (Selected Philosophical Writings, 1893-1913 p. 219), n. 15 ref:45.346:

Kant thought that all syllogisms were reducible to syllogisms in Barbara (the first figure), a point he made in his 1762 memoir On the False Subtlety of the Four Syllogistic Figures. Peirce’s first major logical discovery was that every such reduction takes the logical form of an argument in the figure from which the reduction is made. See his 1866 Memoranda Concerning the Aristotelean Syllogism (W1:505–14 [PDF pp. 549-58]) [=PDF_EXTRA].

cf. "Did Kant think all necessary reasoning is reducible to Barbara syllogisms?"

PDF_EXTRA

06/23/26: 10

no syllogism of the second or third figure can be reduced to the first, without taking for granted an inference which can only be expressed syllogistically in that figure from which it has been reduced.

06/23/26: 10

every figure involves the principle of the first figure, but the second and third figures contain other principles, besides.