Sigmund Freud (6 May 1856 – 23 September 1939), was a Jewish Austrian neurologist who founded the psychoanalytic school of psychiatry. Freud is best known for his theories of the unconscious mind and the defense mechanism of repression, and for creating the clinical practice of psychoanalysis for treating psychopathology through dialogue between a patient, technically referred to as an "analysand", and a psychoanalyst. Freud is also renowned for his redefinition of sexual desire as the primary motivational energy of human life, as well as for his therapeutic techniques, including the use of free association, his theory of transference in the therapeutic relationship, and the interpretation of dreams as sources of insight into unconscious desires. He was an early neurological researcher into cerebral palsy, and a prolific essayist, drawing on psychoanalysis to contribute to the history, interpretation and critique of culture. While many of Freud's ideas have fallen out of favor or been modified by Neo-Freudians, and modern advances in the field of psychology have shown flaws in some of his theories, Freud's work remains influential in the human quest for self-understanding, especially in the history of clinical approaches. In academia, his ideas continue to influence the humanities and social sciences. He is considered one of the most prominent thinkers of the first half of the 20th century, in terms of originality and intellectual influence.