Now it is just the same with logic. If the forms of deductive and inductive reasoning given in the earlier part of this treatise are correct, they constitute a definite addition to logical science, and it would have been absurd to decline to publish such results because I could not at the same time decide in my own mind about the psychology and philosophy of the subject. It comes in short to this, that my book is a book on Formal Logic and Scientific Method, and not a book on psychology and philosophy. It may be objected, indeed, as the *Spectator* objects, that Mill’s System of Logic is particularly strong in the discussion of the psychological foundations of reasoning, so that Mill would appear to have successfully treated that which I feel myself to be incapable of attempting at present. If Mill’s analysis of knowledge is correct, then I have nothing to say in excuse for my own deficiencies. But it is well to do one thing at a time, and therefore I have not occupied any considerable part of this book with controversy and refutation. What I have to say of Mill’s logic will be said in a separate work, in which his analysis of knowledge will be somewhat minutely analysed. It will then be shown, I believe, that Mill’s psychological and philosophical treatment of logic has not yielded such satisfactory results as some writers seem to believe.[18] [18] Portions of this work have already been published in my articles, entitled “John Stuart Mill’s Philosophy Tested,” printed in the *Contemporary Review* for December, 1877, vol. xxxi. p. 167, and for January and April, 1878, vol. xxxi. p. 256, and vol. xxxii. p. 88. (Note added in November, 1878.) Various minor but still important criticisms were made by Professor Robertson, a few of which have been noticed in the text (pp. 27, 101). In other cases his objections hardly admit of any other answer than such as consists in asking the reader to judge between the work and the criticism. Thus Mr. Robertson asserts[19] that the most complex logical problems solved in this book (up to p. 102 of this edition) might be more easily and shortly dealt with upon the principles and with the recognised methods of the traditional logic. The burden of proof here lies upon Mr. Robertson, and his only proof consists in a single case, where he is able, as it seems to me accidentally, to get a special conclusion by the old form of dilemma. It would be a long labour to test the old logic upon every result obtained by my notation, and I must leave such readers as are well acquainted with the syllogistic logic to pronounce upon the comparative simplicity and power of the new and old systems. For other acute objections brought forward by Mr. Robertson, I must refer the reader to the article in question. [19] *Mind*, vol. i. p. 222.