The present volume contains about half of the matter which it was proposed to publish in Volume III of the Work, under the title Real Logic. As much as I regret the necessity of issuing a fourth, still on the whole it is better, since a single third volume would be very bulky, and also since the matter falls naturally into two principal parts. This course enables me to present in this volume the results of the investigation of the problems of practice and the aesthetic, in a form which makes them inde pendently available, without waiting for the preparation, in final form, Of the more philosophical discussions of the theory of reality. It also affords some relief from the necessity of over-compression, of which certain reviewers of Volume II have justly complained. I wish to make very Sincere acknow ledgments to the publishers, in view of their genuine liberality in allowing the work to be extended to four volumes. It is hoped that the concluding part may be ready for publication in about another year.