The other issue is that retarded itself became the clinical term of choice after everyone started using imbecile in a derogatory way. Phrases "mental retardation", "mentally retarded", and "retarded" are subject to the euphemism treadmill: initially used in a medical manner, they gradually took on derogatory connotation, just as did earlier synonyms (for example, moron, imbecile, cretin, dolt and idiot, formerly used as scientific terms in the early 20th century), leading to a search for connotatively neutral replacements Eventually some other word would replace retard anyways.However, the term imbecile quickly passed into vernacular usage as a derogatory term, and fell out of professional use in the 20th century[11] in favor of mental retardation.