Sigmund Freud 
Three Contributions to the Theory of Sex 

A pivotal work in the psychological theories of Sigmund Freud, 'Three Contributions to the Theory of Sex’ puts forth many of the foundational ideas that make up Freud’s theories on sexuality. Freud argues that sexual perversion exists even among the healthy and finds its root in childhood not adolescence. Freud builds upon his 'The Interpretation of Dreams’ by arguing that the unconscious mind plays a significant role in sexual development and that sexuality is a driving force in the development of psychological neuroses.