In 1690, the English philosopher John Locke published his influential work, "An Essay Concerning Human Understanding." He posed a theory that the mind is a blank slate. Thoughts, beliefs, and personality were not innate. Instead, things were learned via the senses and experience. This new understanding was a breakthrough. It set the stage to understand that people can learn. It follows that people can benefit from corrective experiences and therapies. This premise set the stage for the modern conception of psychotherapy and rehabilitation.
Locke was one of the first to differentiate ID from 'madness.' According to Locke: "Herein seems to lie the difference between idiots and madmen. Madmen put wrong ideas together and reason from them. Idiots make very few or no propositions and reason scarce at all (cited in Doll, 1962, p. 23)."
By the end of the Middle Ages, the 'idiots' and the 'insane' were confined to poorly run asylums. These large facilities were basically human warehouses. They offered no useful treatment or education. They served instead to segregate the 'deformed' from 'normal' society. These hospitals were sites of neglect and abuse. The treatment of institutionalized people would be considered obscene by today's standards. Within these neglectful 'hospitals,' people were detained indefinitely. Some have argued that institutions were better than the alternatives. A worse fate was prison or forced prostitution (rape).
Major reforms gradually took place. The medical causes of ID and mental illness became better understood. Medical advances and psychotherapy became the norm of the 20th century. Before such reforms could occur, the cultural understanding of ID had to shift.
In 1797, Swiss physiognomist, Johann Caspar Lavater, wrote Essays on Physiognomy. This book was very influential during the 18th and 19th centuries. Physiognomists believed that people's physical appearances provided insight into their personality. Lavater's book included hundreds of drawings of people depicting various physical features. He related these features to qualities of people's minds, personalities, and motivations.
Lavater's studies affected the treatment of people who committed crimes. He believed that criminal behavior was caused by sickness. Such a person was not at fault for the 'sick' behavior. He postulated that the mind had sections. Each of these sections controlled certain aspects of personality. If a section was not properly developed, the result might be a lack of control over behavior. From this perspective, a person commits a crime because he lacked understanding and control. His actions were not willfully chosen. Lavater's theories ultimately prevented people with ID from suffering the harshest consequences. It helped judges of the day realize that willful disobedience was quite different from poor judgment. This new realization influenced the sentencing imposed on people with ID.
The enlightened writings of Locke and Lavater began to shift European society's view toward people with ID. Unfortunately, this shift was not enough to banish entrenched, prejudicial attitudes. S.G. Howe's On the Causes of Idiocy, (1846) reflected common misconceptions of the time. Howe suggested that IDs and mental illness were caused by a person's actions. The sources of ID were believed to be an unhealthy lifestyle, marriages between blood relatives, heredity, gluttony, and excessive or deviant sexual activity. Such negative attitudes toward people with ID have persisted over the centuries. They can still be readily detected within modern society.
Howe's causal theory of ID was not taken seriously for very long. Nonetheless, he made a lasting contribution to the way that IDs are described. He proposed one of the first classification schemes. It helped to distinguish between the more profoundly impaired individuals from the less impaired folk. Although the labels were pejorative, Howe was one of the first to use severity as a means of classification. For example, Howe referred to the profoundly impaired person as 'heaps of skin and bone in the shape of a human.'