A few words will be enough to put exactly before the reader the object at which the present volume aims. A well-known criticism on the Aristotelian Logic is the complaint, that it provides for the consistency of thought with thought, but not for the consistency of thought with things; that it secures right processes upon given or assumed materials, but does not guarantee the materials upon which the processes are conducted. To supply the want thus indicated, several modern logicians have curtailed or omitted portions of the old Logic, and added new chapters, of which the following headings may serve as specimens, taken from Mr. Bain's work: "Uniformity and Laws of Nature," "Elimination of Cause and Effect," "Experimental Methods," "Frustration of the Methods," "Chance and its Eliminations," "Secondary Laws, Empirical and Derivative," "Explanation of Nature," "Hypotheses," "Classification," "Logic of Mathematics," "Logic of Physics," "Logic of Chemistry," "Logic of Biology," "Logic of Rhetoric," "Logic of Politics," "Logic of Medicine." These titles show the kind of addition that now-a-days is asked, beyond the simple bill of fare found in the Aldrich who satisfied the students of a past generation, and to many even afforded more than they wanted.

It is unfortunate that those who in this country were, perhaps, the loudest in their clamours that logic should take account of the reality which hitherto it had seemed to neglect, should have embraced a system of philosophy which is fatal to firm belief in any reality beyond thought itself. Messrs. Mill and Bain assuredly have not directly tended to take men out of idealism, and make them realists. Yet the former was explicit enough in his demands:^{1} "I conceive it to be true, that Logic is not the theory of thought as thought, but of valid thought: not of thinking, but of correct thinking. . . . In no case can the thinking be valid unless the concepts, judgments, and conclusions resulting from it are conformable to fact. And in no case can we satisfy ourselves that they are so by looking merely at the relations of one part of the train of thought with another. We must ascend to the original sources, the presentations of experience, and examine the train of thought in relation to these."

Little as the modern representatives of the Schoolmen are satisfied, either with the spirit of Mr. Mill's demand, or with the mode of his own response to it, they have deemed it well worth while, not indeed to change the old Logic, but to add to it a new book. Pure Logic remains substantially what it was, and is justified in its position. It assumes, as all other sciences do and must, that human thought has, in general, objective reality; and on this most legitimate assumption it proceeds to lay down the laws of orderly, consistent thinking. The newly added part of Logic, often called Material, Applied or Critical, takes for its special purpose to defend the objective reality of thought. It is thus an assertion of a form of realism, as against idealism, and is called in this book the Philosophy of Certitude. For the whole question comes to this: what reasonable account can be given of man's claim to have real certainty about things? What are the ultimate grounds for holding, that man may regard his knowledge about objects as undoubtedly correct? Scientifically to draw out the account here demanded is a work appositely described by the title, The First Principles of Knowledge.

An endeavour has been made throughout these pages, while stating the sound, traditional principles of certitude, to bring them into constant contact with the antagonist principles, more particularly with the principles of Hume and the pure empirics. It is not true that the only possible philosophy is a history of the opinions which, at various times, have prevailed; but it is true, that the modern spirit will not be satisfied without a statement of how controversies stand on questions which are notoriously disputed. The truth as made manifest in conflict, is what has to be exhibited: and this necessity, whether exactly desirable or not, must stand as explanation or apology to those, whose own special tastes might prompt them to desire a simple exposition of scholastic doctrine apart from the encumbrance of adverse systems. Scholasticism must now be militant, and that, not only with a view to outsiders, but with a view to retaining its own clients, who cannot fail to come across much in modern literature, for the understanding and the consequent rejection of which some direct preparation is needful.

Readers not already familiar with the questions here discussed, would do well at first to leave alone the notes which are printed in smaller type, and concentrate attention on the positive doctrine, the importance of which must be judged, not by the length of its statement, but by the weight of the words. The matter is eminently one which is best conveyed in a few precise sentences, the full import of which must be mastered by leisurely consideration.

{1} Examination, c. xx. pp. 397, seq. (2nd Edit.)