This book is a repudiation of the pessimistic philosophy which regards pleasure as a delusion and life as an unceasing attempt to escape from the 'unpleasure' of the needs and injuries to which the organism is always more or less exposed. Mr. Allen does not believe that these needs and injuries are necessarily unpleasant unless the conations to which they give rise are checked by external circumstances or internal inhibitions. And he thinks that pleasure is to be found not in the attainment of an end, or in the dissipation of a want, but in the successful striving towards these conditions. Thus for Mr. Allen unpleasure and pleasure are not characteristics of those situations which evoke or terminate a series of reactions, but accompaniments of the smooth or impeded functioning of such a series.