I suggest that the problem of the possibility of knowledge is but an aspect of the question of the relation of knowing to acting, of theory to practice. The distinctions which the philosophers raise, the oppositions which they erect, the weary treadmill which they pursue between sensation and thought, subject and object, mind and matter, are not invented _ad hoc_, but are simply the concise reports and condensed formula of points of view and practical conflicts having their source in the very nature of modern life, conflicts which must be met and solved if modern life is to go on its way untroubled, with clear consciousness of what it is about. As the philosopher has received his problem from the world of action, so he must return his account there for auditing and liquidation. More especially, I suggest that the tendency of all the points at issue to precipitate in the opposition of sensationalism and rationalism is due to the fact that sensation and reason stand for the two forces contending for mastery in social life: the radical and the conservative. The reason that the contest does not end, the reason for the necessity of the combination of the two in the resultant statement, is that both factors are necessary in action; one stands for stimulus, for initiative; the other for control, for direction. I cannot hope, in the time at my command this evening, to justify these wide and sweeping assertions regarding either the origin, the work, or the final destiny of philosophic reflection. I simply hope, by reference to some of the chief periods of the development of philosophy, to illustrate to you something of what I mean.