taken from a different point of view from mine, and expressed with far greater asperity than I should myself think justifiable; legitimated, no doubt, to the writer's mind by "a certain vein of disingenuousness" which he finds in Sir W. Hamilton, but which I have not found, and shall not believe until I see it proved.

I must have been quite incapable of profiting by criticism, if I had learned nothing from assailants so numerous, all of more or less, and some of very considerable, ability. They have detected not a few inadvertences of expression, as well as some of thought: and partly by their help, partly without it, I have discovered others. They have not shaken any statement or opinion of real moment; but I am sincerely indebted to them, both for the errors they have corrected, and for compelling me to strengthen my defences. The point in which it was to be expected that they would oftenest prevail, was in showing me to have erroneously interpreted Sir W. Hamilton. The difficulty to any thinker is so great, in these high regions of speculation, of placing himself completely at the point of view of a different philosophy, and even of thoroughly understanding its language, that it would be very presumptuous in me to imagine that I had always overcome that difficulty; and that too with the warning before me, of the absolute failure of able and accomplished minds on the other side in philosophy, to accomplish this in regard to the modes of thinking with which I am most familiar. I have been surprised, therefore, to find in how few instances, and those how little important, the defenders of Sir W. Hamilton have been able to show that I have misunderstood or incorrectly stated his opinions or arguments. I cannot doubt that more such mistakes remain to be pointed out: and I regret that the greater part of the volume has not yet, in its relation to Sir W. Hamilton, had the benefit of a

sufficiently minute scrutiny. Had the unsparing criticism of Mr. Mansel on the first few chapters been continued to the remainder, he would doubtless have pointed out real mistakes; he might perhaps have thrown light on some of the topics from his own thoughts; and I should at least have had to thank him for additional confidence in the statements and opinions which had passed unharmed through the ordeal of his attacks.

Where criticism or reconsideration has convinced me that anything in the book was erroneous, or that any improvement was required in the mode of stating and setting forth the truth, I have made the requisite alterations. When the case seemed to require that I should call the reader's attention to the change, I have done so; but I have not made this an invariable rule. Mere answers to objectors I have generally relegated to notes. With so many volumes to deal with, I could not take express notice of every criticism which they contained. When any of my critics finds that he, or some of his objections, are not individually referred to, let him be assured that it is from no disrespect, but either because I consider them to have been answered by the reply made to some one else, or because their best confutation is to remand the objector to the work itself, or because the edge of the objection has been turned by some, perhaps quite unapparent, correction of the text. A slight modification in a sentence, or even in a phrase, which a person acquainted with the former editions might read without observing it, and of which, even if he observed it, he would most likely not perceive the purpose, has sometimes effaced many pages of hostile criticism.

Of the assailants to whom I replied, two only have published a rejoinder; Dean Mansel, in the Contemporary Review for September 1867, and Dr. M'Cosh, in the British and Foreign Evangelical Review for April 1868. Neither of them appears to me to have added much of value to what he had previously advanced; and so far as concerns Dean Mansel, his regretted death has put a final termination to the controversy between us. I am not, however, thereby exempted from taking notice, however briefly, of such points in his rejoinder as appear to require it. Dr. M'Cosh seems to think it a great triumph of his assaults upon me, that many of them were not noticed in my replies to critics. It is a little unreasonable in Dr. M'Cosh to suppose that in a work, the subject of which is the philosophy of Sir William Hamilton, I was bound to fight a pitched battle with Dr. M'Cosh on the whole line. His book was an attack directed against the whole of my philosophical opinions. I answered such parts of it as had reference to the present work, when they seemed to require an answer, and not to have received it sufficiently in what I had already written. And I have done the same, in the present edition, with his rejoinder.

Besides several unpublished criticisms which I owe to the kindness of correspondence, and which have helped me to correct or otherwise improve some of the details of the work; two more attacks have been made upon it subsequently to the third edition. Professor Veitch, in the Appendices to his interesting Memoir of Sir W. Hamilton, has commented sharply on what I have said respecting Sir W. Hamilton's mode of understanding the Relativity of human knowledge, and respecting his failure to apprehend correctly the general character of Hume and Leibnitz as philosophers, as well as some particular passages of Aristotle. of Aristotle. On the first subject, that

of Relativity, I find so much difficulty in reducing Professor Veitch's statement to distinct propositions, and, so far as I understand his meaning, it differs so little, and that little not to its advantage, from what I have already commented on in answering Mr. Mansel, that I do not think it necessary to burthen this volume with an express reply to him. With regard to Hume and Leibnitz I am content that they who have a competent knowledge of those philosophers should form their own opinion. As regards Sir W. Hamilton's interpretation of Aristotle, Professor Veitch has convicted me of a mistake in treating a citation made by his editors as if it had been made by himself, and of an overstatement of one of Sir W. Hamilton's opinions which I only noticed incidentally. These errors I have corrected, in their places, and it will be found that they do not affect anything of importance in the criticism there made upon Sir W. Hamilton.

Professor Veitch* considers it unfair that I should press against Sir W. Hamilton anything contained in his Lectures, these having been hastily written under pressure from time, and not being the most matured expression of some of his opinions. But though thus written, it is admitted that they continued to be delivered by Sir W. Hamilton as long as he performed the duties of Professor; which would not have been the case if he had no longer considered them as a fair representation of his philosophy. A complete representation I never pretended that they were; a correct representation I am bound to think them; for it cannot be believed that he would have gone on delivering to his pupils matter which he judged to be inconsistent with the subsequent developments of his philosophy.

The other thinker who has taken the field against my psychological opinions is Dr. Ward, who, in the Dublin * Memoir of Sir William Hamilton, pp. 212, 213.

Review for October 1871, has made an able attack on the views I have expressed in this and other writings on the subject of what is called Necessary Truth. Some of Dr. Ward's observations are more particularly directed against a portion of my System of Logic, and the fittest place for their discussion is in connection with that treatise. But the greater part of his article principally regards the chapter of the present work which relates to Inseparable Association, and a reply to it will be found in a note which I have added at the end of that chapter.