Prior to Howe's On the Causes of Idiocy (1845) people with intellectual disabilities were considered indistinguishable from one another. This was true regardless of varying degrees of impairment. Although Howe's theory was prejudicial and incorrect, he was the first to offer a classification scheme according to severity.
According to Howe (1846), Fools were a subdivision of Idiots. Idiots had some muscular control and some cognitive functioning. This group was thought to have almost no reasoning skills and major delays in speech.
Howe's third division was the Simpletons. This group possessed motor skills and adequate reasoning skills. They could complete daily activities with little guidance. However, they had difficulty functioning within society.
Alongside Howe's Idiots, Fools, and Simpletons, other terms were also historically used to describe varying degrees of severity. Originally, these neutral words referred to categories within a classification scheme. However, as the terms entered the vernacular, they took on a prejudicial meaning with a stigmatizing effect. Here are some other obsolete, classification terms for intellectual disability. These terms no longer have any legitimate medical meaning. However, they are still used as insults.
Cretin is a very old term. It is thought to come from the French word meaning Christian. This term originally reflected the notion that people with IDs were still Christians. Thus, they should be treated with kindness. Ironically, in today's language this term has negative connotation. Its meaning is derogatory.
The term amentia has a long history. It is mostly associated with dementia. The difference between amentia and dementia was age. Amentia was used when someone developed deficits in mental functioning early in life. In contrast, dementia was used when someone developed mental deficiencies during adulthood. During the 1890s, amentia was used to describe someone born with mental deficiencies. By 1912, ament was a label lumping "idiots, imbeciles, and feeble minded" into a single category. It was distinct from a dement. This was a label reserved for mental problems developing later in life.
The term dementia is unique. Its meaning has not changed in hundreds of years. The term first emerged during the 16th century. It was used in reference to people who lost mental functioning. In 1912, the term dement was used to classify people who lost their previous level of functioning. Today, the term dementia retains a similar meaning. However, in DSM-5 (APA, 2013) dementia was relabeled neurocognitive disorder.
Idiot is derived from the Greek language. It was used to classify people with severe intellectual disabilities. It referred to people who could not take care of themselves and required 24-hour care. The term gradually became mainstreamed. By the mid-1890s, its derogatory usage caused the medical community to discontinue its use.
Imbecile is a French term. It is derived from a Latin word meaning "without support." The term originally referred to someone who was physically weak. This term was used from the mid-16th century, to the early 19th century. Imbecile was a medical term to classify people with moderate ID. Like the term idiot, it gradually entered the vernacular and became a term of abuse.
Mongolism (or mongoloid) was a medical term. It was used to identify someone with Down syndrome. For obvious reasons, the Mongolian People's Republic objected to this use. They requested that the medical community cease the use of this term. Their request was granted in the 1960s. The World Health Organization agreed that the term should no longer being used within the medical community.