Intellectual disability  

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Ship of Fools  by Hieronymus Bosch
Ship of Fools by Hieronymus Bosch

"To be stupid, and selfish, and to have good health are the three requirements for happiness; though if stupidity is lacking, the others are useless" [...] --G. Flaubert

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Intellectual disability is a generalized disorder appearing before adulthood, characterized by significantly impaired cognitive functioning and deficits in two or more adaptive behaviors, commonly known in the late twentieth century as mental retardation (MR). It was historically defined as an intelligence quotient score under 70. Once focused almost entirely on cognition, the definition now includes both a component relating to mental functioning and one relating to individuals' functional skills in their environment. As a result, a person with an unusually low IQ may not be considered intellectually disabled. Syndromic mental retardation is intellectual deficits associated with other medical and behavioral signs and symptoms. Non-syndromic mental retardation refers to intellectual deficits that appear without other abnormalities.

Traditional terms

The three traditional terms denoting varying degrees of mental deficiency long predate psychiatry. They were originally used in English as simple forms of abuse, and this is still the main usage. Their now obsolete use as psychiatric technical definitions is of purely historical interest. There have been some efforts made among mental health professionals to discourage use of these terms.

  • Idiot stems from Gr. Idiotos - someone who does not participate in politics. The term now indicates the greatest degree of mental deficiency, where the mental age is 2 years or less, and the person cannot guard himself against common physical dangers. The term is gradually being replaced by the term profound mental retardation.
An 'idiot' is the corresponding term for a person affected by idiocy.
The word idiot comes from the Greek word ιδιωτης, idiôtês, "a private citizen, individual", from ιδιος, idios, "private". In ancient Athens, an idiot was a person who declined to take part in public life, such as democratic city government. Since such activities were honorable and could directly affect all citizens, idiot was a term of derision.
  • Imbecility was a type of mental deficiency less extreme than idiocy and not necessarily inherited. It is now usually subdivided into two categories, known as severe mental retardation and moderate mental retardation.
  • Moron was defined by the American Association for the Study of the Feeble-Minded in 1910, following work by Henry H. Goddard, as the term for an adult with a mental age between eight and twelve; mild mental retardation is now the more widely-accepted term for this condition. Alternative definitions of these terms based on IQ were also used. For example, the following data based on the Wechsler adult IQ test (WAIS) were used in 1958:
Idiotbelow 20
Borderline deficiency70-79

Today the following ranges are in standard use:

Profound mental retardationbelow 20
Severe mental retardation20-34
Moderate mental retardation35-49
Mild mental retardation50-69
Borderline deficiency70-79

In other Westen nations, such as Australia, New Zealand and Great Britain, the term Mental Retardation is now considered Politically incorrect. The term Intellectual Disability is currently favoured.


  • Wechsler, David The Measurement of Adult Intelligence (1944), Baltimore, The Williams & Wilkins Company.

Unless indicated otherwise, the text in this article is either based on Wikipedia article "Intellectual disability" or another language Wikipedia page thereof used under the terms of the GNU Free Documentation License; or on research by Jahsonic and friends. See Art and Popular Culture's copyright notice.

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