The most serious objections which have been brought against my treatment of logic have regard to my failure to enter into an analysis of the ultimate nature and origin of the Laws of Thought. The *Spectator*,[16] for instance, in the course of a careful review, says of the principle of substitution, “Surely it is a great omission not to discuss whence we get this great principle itself; whether it is a pure law of the mind, or only an approximate lesson of experience; and if a pure product of the mind, whether there are any other products of the same kind, furnished by our knowing faculty itself.” Professor Robertson, in his very acute review,[17] likewise objects to the want of psychological and philosophical analysis. “If the book really corresponded to its title, Mr. Jevons could hardly have passed so lightly over the question, which he does not omit to raise, concerning those undoubted principles of knowledge commonly called the Laws of Thought.... Everywhere, indeed, he appears least at ease when he touches on questions properly philosophical; nor is he satisfactory in his psychological references, as on pp. 4, 5, where he cannot commit himself to a statement without an accompaniment of ‘probably,’ ‘almost,’ or ‘hardly.’ Reservations are often very much in place, but there are fundamental questions on which it is proper to make up one’s mind.” [16] *Spectator*, September 19, 1874, p. 1178. A second portion of the review appeared in the same journal for September 26, 1874, p. 1204. [17] *Mind*: a Quarterly Review of Psychology and Philosophy. No. II. April 1876. Vol. I. p. 206.