OF the essays published in this volume about one-half are new. The others have already appeared during the past five years in various scientific periodicals, like the Political Science Quarterly, Quarterly Journal of Economics, Yale Review and Journal of the Social Science Association, but have been revised and brought down to date. Although nominally disconnected, the essays, new and old, which are here printed, will, I trust, be found not to be entirely lack ing in continuity, or unworthy of the more permanent form which they now assume. Although they were written primarily from the American point of view, I venture to hope that the discussions of theory may prove to be of a wider interest.
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