An essential part of the theory of wages here stated was presented in a paper read before the American Economic Association, in December, 1888, and published in a monograph of the American Economic Association in March, 1889; and other parts of this theory were issued at intervals following that date. The theory of value was published in the _New Englander_ for July, 1881. I had not then chanced to see the early statements of the principle of marginal appraisal contained in the works of Von Thuenen and Jevons, and did not consciously borrow anything from their writings, but I gladly render to them the credit that is their due. I do not fear that I shall be supposed to have borrowed other parts of the general theory here offered. The theory of capital here stated was first presented in a monograph of the American Economic Association for May, 1888, and the discussion of money of which the present work gives a summary, in articles in the _Political Science Quarterly_ for September, 1895, and for June and September, 1896. The discussion of the relation of protective duties to monopoly appeared in the same quarterly for September, 1904. The author should, perhaps, apologize for the fewness of the citations from other works which this volume contains. The richness of the recent literature of Economic Theory, especially in America, would have made it necessary to use much space if the resemblances and the contrasts presented by points in this volume, and corresponding points in other volumes, had been noted. Worthy of special attention, if citations had been given, would have been the writings of Professors Irving Fisher, Simon N. Patten, and Frank A. Fetter of this country, and Professor Friedrich von Wieser of Prague, who have worked in various parts of the same field in which the studies here offered belong, and also those of Minister Eugen von Boehm-Bawerk of Vienna, who has treated some of the same themes in a strongly contrasted way. If merited attention were paid to the works of Hadley, Taussig, Carver, Seligman, Giddings, Seager, Walker, and a host of eminent foreign scholars, a large part of the space in the book would have to be thus preempted. I desire most gratefully to acknowledge the assistance which in the preparation of this book I have received from my colleague, Professor H. L. Moore of Columbia University, from my son, Mr. John Maurice Clark, Fellow in Economics in Columbia University, and from my former colleague, Professor A. S. Johnson of the University of Nebraska. Besides reading the manuscript and offering valuable suggestions, Professor Johnson has kindly taken upon himself the reading of the proof. JOHN BATES CLARK. CONTENTS