James Cowles Prichard advanced a similar concept he called moral insanity, which would be used to diagnose patients for some decades. Moral in this sense referred to affect (emotion or mood) rather than ethics, but it was arguably based in part on religious, social and moral beliefs, with a pessimism about medical intervention so social control should take precedence. These categories were much different and broader than later definitions of personality disorder, while also being developed by some into a more specific meaning of moral degeneracy akin to later ideas about psychopaths. Separately, Richard von Krafft-Ebing popularized the terms sadism and masochism, as well as homosexuality, as psychiatric issues. The German psychiatrist Koch sought to make the moral insanity concept more scientific, and in 1891 suggested the phrase psychopathic inferiority, theorized to be a congenital disorder. This referred to continual and rigid patterns of misconduct or dysfunction in the absence of apparent "mental retardation" or illness, supposedly without a moral judgment. Described as deeply rooted in his Christian faith, his work established the concept of personality disorder as used today. 20th century
In the early 20th century, another German psychiatrist, Emil Kraepelin, included a chapter on psychopathic inferiority in his influential work on clinical psychiatry for students and physicians. He suggested six types – excitable, unstable, eccentric, liar, swindler and quarrelsome. The categories were essentially defined by the most disordered criminal offenders observed, distinguished between criminals by impulse, professional criminals, and morbid vagabonds who wandered through life.
Gordon Allport published theories of personality traits from the 1920s—and Henry Murray advanced a theory called personology, which influenced a later key advocate of personality disorders, Theodore Millon. Tests were developing or being applied for personality evaluation, including projective tests such as the Rorschach test, as well as questionnaires such as the Minnesota Multiphasic Personality Inventory. Around mid-century, Hans Eysenck was analysing traits and personality types, and psychiatrist Kurt Schneider was popularising a clinical use in place of the previously more usual terms character, temperament or constitution. American psychiatrists officially recognized concepts of enduring personality disturbances in the first Diagnostic and Statistical Manual of Mental Disorders in the 1950s, which relied heavily on psychoanalytic concepts. Somewhat more neutral language was employed in the DSM-II in 1968, though the terms and descriptions had only a slight resemblance to current definitions. The DSM-III published in 1980 made some major changes, notably putting all personality disorders onto a second separate axis along with "mental retardation", intended to signify more enduring patterns, distinct from what were considered axis one mental disorders. Inadequate and asthenic personality disorder categories were deleted, and others were expanded into more types, or changed from being personality disorders to regular disorders. Sociopathic personality disorder, which had been the term for psychopathy, was renamed Antisocial Personality Disorder. Most categories were given more specific operationalized definitions, with standard criteria psychiatrists could agree on to conduct research and diagnose patients. In the DSM-III revision, self-defeating personality disorder and sadistic personality disorder were included as provisional diagnoses requiring further study.