As described in his book "The Interpretation of Dreams," Sigmund Freud thought all dreams were unconscious expressions of wish fulfillment. According to the book, because the unconscious contained ideas and images that were often disturbing, it would censor, or filter, the information before the conscious became aware of it.
As Freud explains in "The Interpretation of Dreams," to understand dreams, they must be decoded, or interpreted. The outward content of a dream also has a latent meaning. Four principles help discover this. Condensation fuses various psychic elements together. Displacement refers to the lack of focus in dreams, and how one symbol can substitute for another, such as a king for someone's father. Representation changes abstract thoughts into images, and free association helps in the interpretation of the images back into understandable form. Finally, secondary revision creates organization in a dream by supplying narrative coherence.
First published in 1900, "The Interpretation of Dreams" remained unknown for many years. However, once Freud became more well-known, the book became popular as well. According to Encyclopedia Britannica, though Freud's theories are controversial, they remain influential due to the power of his vision and intellectual legacy. He greatly influenced psychology through his development of psychoanalysis, of which dream interpretation was a part.