Definitions of Mental Retardation:

A Chronological List with Dates and References

1. An idiot is one who hath no understanding from his nativity. Prerogative of the King of England, 1255 to 1290 A. D. (Payne and Patton, 1981)

The word idiot is derived from the Latin word idiota, meaning an ignorant person and from the Greek word idiotos, meaning unfit for public life. It was used to refer to individuals with mental retardation (of all levels) well into the 20^th Century.

2. An idiot is such a person who cannot account or number, nor can tell who was his father or mother, nor how he, so as it may appear he has not understands or reason of what shall be his profit or his loss. Sir Anthony Fitzherbert, about 1510 to 1520 (Payne and Patton, 1981).

Sir Anthony Fitzherbert was an English judge who was appointed the king’s serjeant-at-law on 18 November, 1510. His work, La Graunde Abridgement, was the first systematic attempt to provide a summary of English law.

3. Idiocy  is a specific infirmity of the cranio-spinal axis, produced by deficiency of nutrition in utero and neo-anti. It incapacitates mostly the functions which give rise to the reflex, instinctive and conscious phenomena of life; consequently, the idiot moves, feels, understands, wills but imperfectly; does nothing, thinks of nothing, cares for nothing (extreme cases), he is legally irresponsible, isolated without associations; a soul shut up in imperfect organs an innocent.

Edouard Seguin, France/United States, 1866.

Edouard Seguin was an associate of Jean Itard, whose work with Victor, the Famouse “Wild Boy of Aveyron” was the first documented (but unsuccessful) attempt to educate a child thought to have idiocy (mental retardation). Seguin became head teacher of a class of idiot children at salpetriere, France and later started a private school for idiots. He later moved to the United States, where in 1866 he published his famous work, Idiocy: and its Treatment by the Physiological Method, in which the above definition appeared. In 1876, Seguin became the first president of The Association of Medical Officers of American Institution for Idiotic and Feeble-Minded Persons, which evolved into the American Association on Mental Retardation.

4. Idiocy (involves) deficiency in the ordinary mental powers, due to disease or failure of development of the central nervous system. More especially, idiocy often relates to the severer forms of such mental deficiency, while children of subnormal capacity or backward development are spoken of as feeble-minded, or children. There is some tendency to use the term feeble-minded to include all degrees of defect from the slightest to the most severe. (James Mark Baldwin, Canada, 1901).

James Mark Baldwin founded the first psychological laboratory in the British Empire in 1889 at the University of Toronto. His most famous work, Mental Development in the Child and the Race, first published in 1895 is recognized as an important text in the history of social psychology.

5. Mental Deficiency: A state of incomplete mental development of such a kind and degree that the individual is incapable of adapting himself to the normal environment of his fellows in such a way to maintain existence independently of supervision, control or external support. (Tredgold, Great Britain, 1937).

A. F. Tredgold was a member of the Britich Eugenics Society, which like its counterpart in the United States favored reducing or eliminating reproduction by those deemed unfit through segregation and sterilization. In his article “The Feebleminded -  A Social Danger,” which appeared in Eugenics Review, (1909), Tredgold wrote, “…in the animal world or in a primitive state of human society these degenerate members would very soon by extinguished …. Our modern legislation … is actually tending to breed degenerates.” (Eugenics Watch U.K)

6. Six criteria … have been generally considered essential to an adequate definition and concept (of Mental Deficiency): These are 1) social incompetence;

2) Mental sub normality; 3) which has been developmentally arrested; 4) which obtains at maturity; 5) is of constitutional origin; and 6) is essentially incurable. E. A. Doll, United States, 1941 (Doll, 1941, p.215).                       

Edgar Doll is best known for his work at the Vineland Training School where he developed the Vineland Social Maturity Scale (now the Vineland Adaptive Behavior Scales). First published in 1935, this instrument was designed to assess the daily living skills of individuals with mental retardation.

7. Mental Retardation refers to significantly sub average general intellectual functioning which originates during the developmental period and is associated with impairment in adaptive behavior. 

Sub average intellectual Functioning: one or more standard deviations (SD’s) below the mean. (An IQ score of 85 or below)

Adaptive Behavior: adaptation to the demands of the environment.

Developmental Period: birth to age 16.

American Association on Mental Deficiency, United States, 1961 (Heber, 1961)

This definition, with its three components (sub average intelligence, impaired adaptive behavior, and origination during the developmental period), became widely accepted. Subsequent AAMD/AAMR definitions are essentially refinements of Heber’s 1961 definition.

8. Mental Retardation refers to significantly sub-average general intellectual functioning existing concurrently with deficits in adaptive behavior and manifested during the developmental period. Sub-Average Intellectual Functioning: at least two standard deviations below the mean (current functioning – not permanent status). (an IQ of 70 score or below)

Adaptive Behavior: ability to meet the standards of personal independence and social responsibility expected of his/her level and cultural group.

The 1973, definition through retaining the three basic AAMR components, makes the following significant changes:

1) defining “sub-average intelligence” as rather than one standard deviation below the mean (85). This reduced the number of individuals who met this criterion from 16% of the population to a little more than 2% of the population;

2) clarifying the meaning of deficient adaptive behavior; and

3) extending the developmental period to age 18.

9. Mental Retardation refers to significantly sub-average general intellectual functioning existing concurrently with deficits in adaptive behavior and manifested during the developmental period. Sub-average Intellectual Functioning: two or more standard deviations below average but a small number of persons with scores up to 10 points above the guideline ceiling may be classified as mildly mentally retarded if their adaptive behavior is significantly impaired (current functioning – not permanent status)

American Association on Mental Deficiency, United States, 1977 (Grossman, 1977)

This 1977 revision allows for individuals with borderline intelligence (70 to 80) to be classified as having mental retardation and thus makes them eligible for services provided to those with MR, including special education.

10. Mental Retardation refers to substantial limitations in present functioning. It is characterized by significantly sub-average general intellectual functioning existing concurrently with related limitations in two or more of the following applicable adaptive skills areas: communication, self care, home living, social skills, self direction, health and safety, functional academics, leisure and work. Mental retardation manifested before age 18.

Significantly Sub average Intellectual Functioning: same as 9 (An IQ Score of 70-80 or below)

American Association on Mental Retardation, United States, 1992 (AAMR, 1992)

This AAMR definition, through still retaining Heber’s three components, provides even more specificity regarding the meaning of the phrase “deficits in adaptive behavior.” Other changes, particularly in regard to level of mental retardation. Though not part of definition, are included in the AAMR publications, Mental Retardation: Definition, classification, and systems of supports, in which the new definition appear. Click here for an ERIC Clearing house article which summarizes differences between the current AAMR definition and previous ones.

11. Mental Retardation is a disability characterized by significant limitation both in intellectual functioning and in adaptive behavior as expressed in conceptual, social, and practical adaptive skills. This disability originates before the age of 18.

Significant Limitations in Intellectual Functioning: same as 9.