Havelock Ellis 
Psychology of sex vol III: analysis of the sexual impulse 

The present volume of Studies deals with some of the most essential problems of sexual psychology. The Analysis of the Sexual Impulse is fundamental. Unless we comprehend the exact process which is being worked out beneath the shifting and multifold phenomena presented to us we can never hope to grasp in their true relations any of the normal or abnormal manifestations of this instinct. I do not claim that the conception of the process here stated is novel or original. Indeed, even since I began to work it out some years ago, various investigators in these fields, especially in Germany, have deprived it of any novelty it might otherwise have possessed, while at the same time aiding me in reaching a more precise statement. This is to me a cause of satisfaction. On so fundamental a matter I should have been sorry to find myself tending to a peculiar and individual standpoint. It is a source of gratification to me that the positions I have reached are those toward which current intelligent and scientific opinions are tending. Any originality in my study of this problem can only lie in the bringing together of elements from somewhat diverse fields. I shall be content if it is found that I have attained a fairly balanced, general, and judicial statement of these main factors in the sexual instinct.