necessity of the Kantian answer has been so little appreciated. To trace the origin and bring out the points of the question, in order to the exhibition of that necessity, will be the object of the following treatise. To do this thoroughly, indeed, would carry us back through Hobbes to Bacon. But as present limits do not allow of so long a journey, we must be content with showing Hume’s direct filiation to Locke, who, indeed, sufficiently gathered up the results of the ‘empirical’ philosophy of his predecessors. Distinction between literary history and the history of philosophical systems. 4. Such a task is very different from an ordinary undertaking in literary history, and requires different treatment. To the historian of literature a philosopher is interesting, if at all, on account of the personal qualities which make a great writer, and have a permanent effect on letters and general culture. Locke and Hume undoubtedly had these qualities and produced such an effect--an effect in Locke’s case more intense upon the immediately following generations, but in Hume’s more remarkable as having reappeared after near a century of apparent forgetfulness. Each, indeed, like every true philosopher, was the mouth-piece of a certain system of thought determined for him by the stage at which he found the dialectic movement that constitutes the progress of philosophy, but each gave to this system the stamp of that personal power which persuades men. Their mode of expression had none of that academic or ‘ex cathedra’ character, which has made German philosophy almost a foreign literature in the country of its birth. They wrote as citizens and men of the world, anxious (in no bad sense) for effect; and even when their conclusions were remote from popular belief, still presented them in the flesh and blood of current terms used in the current senses. It is not, however, in their human individuality and its effects upon literature, but as the vehicles of a system of thought, that it is proposed here to treat them; and this purpose will best be fulfilled if we follow the line of their speculation without divergence into literary criticism or history, without remarks either on the peculiarities of their genius or on any of the secondary influences which affected their writings or arose out of them. For a method of this sort, it would seem, there is some need among us. We have been learning of late to know much more about philosophers, but it is possible for knowledge about philosophers to flourish inversely as the knowledge of philosophy. The revived interest which is noticeable in the history of philosophy may be an indication either of philosophical vigour or of philosophical decay. In those whom intellectual indolence, or a misunderstood and disavowed metaphysic, has landed in scepticism there often survives a curiosity about the literary history of philosophy, and the writings which this curiosity produces tend further to spread the notion that