Bifur is NOT mentally disabled.

Bifur has a frontal-lobe brain injury which interferes with his cognitive abilities. This is not the same thing as being “mentally retarded” “intellectually disabled” or the various other synonyms for someone with a mental handicap.

This confusion stems from a common misunderstanding about the differences between brain injuries and lifelong cognitive impairment. This is a good opportunity to clarify what exactly constitutes mental retardation, how a frontal lobe injury like Bifur’s would affect the brain, and how people frequently confuse the two.

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The definition of “mental retardation” from wikipedia:

[Mental retardation] is a generalized disorder appearing before adulthoodcharacterized by significantly impaired cognitive functioning and deficits in two or or more adaptive behaviors

Therefore, one would not diagnose Bifur as being mentally handicapped or having an intellectual disability. Presumably his IQ is exactly the same as it was before his injury.

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It’s a good thing Dwarves have thick skulls, which probably saved Bifur from more extensive frontal-lobe damage or death. In non-mythical humans, the frontal lobes of the brain handle the higher functions: movement and agility, memory, and language. Personality and mood are also affected. Intelligence is not. 

The peculiar quirk to a left-lobe brain injury like Bifur’s is damage to the part of the brain which processes speech. Language comprehension actually occurs deeper within the brain. This is why his language abilities are limited to Khuzdul & iglishmek, but he can still comprehend what others are saying in the common language. 

So besides the occasional necessary prodding from his cousins when he’s spacing out, the occasional mood swing, an inability to speak the common tongue, and a newfound penchant for green leafy vegetables, Bifur’s a fairly normal dwarf.

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So really, what the confusion boils down to is the confounding of injury vs lifelong systemic dysfunction. Bifur’s brain injury  intellectual handicap.

According to a study done by the University of Bristol in regards to the public perception of those with brain injuries, the confusion is quite common.

The major themes that emerged from the analysis were: inaccurate beliefs about recovery time and possible extent of recovery from brain injury; lack of awareness of the diversity of problems it can cause, particularly the existence of behavioural and cognitive sequelae; misconceptions about the capabilities of brain-injured people depending on the visibility or invisibility of their disability; and misidentification of brain-injured individuals as mentally ill or learning disabled.

hey, sounds like our Bifur!!