Difficulties with the WHO Definitions

There are two main deficiencies in the definitions given above that should be remedied. First, they contain no account of what is normal or abnormal for human beings either in structure and function (as in the definition of impairment) or in the manner and range of performing an activity (as in the definition of disability). Second, only the definition of a handicap makes reference to disadvantage, yet intuitively, disadvantage, or at least inconvenience, is part of the concept of disability. Below are suggested improvements, although significant imperfections remain.

THE HUMANLY NORMAL AND ABNORMAL. An account of the type of abnormality necessary for the notion of impairment to be applicable is needed. What is normal human physiology, psychology, anatomic structure, and function? The topic is vast and controversial, and it is easy to go wrong.

A statistical account of normal structure and function would be misconceived. Even if all human beings were damaged in a nuclear accident, it would not be humanly normal to suffer from radiation sickness and sterility.

It is also not possible to define normal structure and function simply by listing all the body parts human beings are observed to have, what those parts are observed to do, and how they do it. This is not only because knowledge in this area is incomplete. If one simply observes human organisms, the list will include things frequently observed that never would count as normal. One would observe both sound and decayed teeth, both painful childbirth and painful urination, and both the beating of the heart and myocardial infarction (another thing the heart is seen to do), yet the second item in each pair is abnormal. The concept of a human organ and its function is inseparable from the concept of what is normal for human beings (an evaluative, teleological concept), and any definition of normality that refers to the functions of organs assumes the concept of the normal in the attempt to define it. (The biologist's concept of the function of an organ need not depend on cultural assumptions, however. It only presupposes the distinction between normal and abnormal.)

A partial account of the normal functions and abnormalities of body parts can be derived from an understanding of their role in the survival of the species. As Norman Daniels puts it (p. 28), the biomedical sciences, including evolutionary biology, provide an account of "the design of the organism" and "its fitness to meeting biological goals" relative to which a scientist can specify some normal and abnormal phenomena. However, the usual biological goal assumed in evolutionary theory—transmission of an organism's genes to the next generation—does not entail the abnormality of many intuitively abnormal conditions, such as the diseases of extreme old age.

Rather than abandon hope of a definition, though, it is possible to adopt the following crude and incomplete standard, which suffices for the issues surrounding impairment and disability and leaves the thorniest controversies aside. A state of a human being is an abnormality of the type that can make it an impairment only if the state is such that if all human beings had had it from the beginning of human prehistory and otherwise were as they in fact are now, the human species would have been significantly less likely to survive.

This is a necessary but not a sufficient condition of a state's being abnormal. That is, all abnormal traits are ones that probably would have precluded species survival, but not all states that would have precluded species survival are abnormal. States that are abnormal fulfill certain other conditions. There is no complete list of these conditions, but here are two of them.

The first requires a subsidiary definition. Some traits assist survival when they are present in some members of a population as long as other individuals have a different trait; however, if all individuals had the trait, the population could not survive. These can be called diversity-requiring traits. An obvious one is being male or female. Having some males has been indispensable to the species's survival over time, but if all individuals were male (from prehistory), the species would have died out long ago.

The other condition excludes from the definition characteristics that are universal in but are limited to human beings of a certain developmental stage. It is normal for newborn infants to be unable to walk, for example, even though if all human beings of all ages had always been unable to walk, the species would not have survived.

The definition of abnormality can be supplemented in light of this characterization. Thus, a state of a human being is an abnormality of the type relevant to impairment only if the state is such that if all human beings had had it from the beginning of human prehistory and otherwise were as they in fact are today, the human species would have been unlikely to survive. If the state (1) is of that kind, (2) is not a diversity-requiring trait, and (3) is not a trait that is characteristic of and limited to certain stages of human development, it is abnormal.

With this understanding of abnormality, one can say, with the WHO, that an impairment is any abnormal loss or other abnormality of psychological, physiological, or anatomic structure or function. This standard ensures that the abnormalities that qualify as impairments are ones that characteristically make a difference in living a human life, the typical life of the species, whether or not they cause a great loss for any specific individual in any particular set of circumstances. Thus, extreme myopia (nearsightedness or shortsightedness) is an impairment by this definition because if all human beings had had this characteristic since prehistory and otherwise had been the same as they are today, the human species would have been unlikely to survive. A hunter-gatherer society composed entirely of severely myopic people would be doomed. Yet severe myopia may not cause serious inconvenience to a person in a modern technological society.

IMPAIRMENT AND DISABILITY. The WHO definition of disability says nothing about disadvantage, whereas intuitively that seems to be part of the concept. People would not count it as a disability if someone were unable to perform an activity in the manner normal for human beings if it were an activity that that person, or perhaps everyone, had no interest in performing in that way. It is no disability to someone who has taken a vow of celibacy or has undergone voluntary surgical sterilization that that person is biologically infertile because it does not disadvantage that person even though it is an impairment.

Instead, one can define a disability as any impairment-caused disadvantageous restriction or lack of ability to perform an activity in the manner or within the range that is normal for a human being. The relevant notion of normality is the same one identified above: that manner and range of activity without which the human species as a whole would have been unlikely to survive. Thus, extreme myopia, although it is an impairment, is not a disability for someone who suffers no consequent disadvantage because she or he has glasses or contact lenses that enable her or him to see perfectly.

Some people argue that a disability need not be disadvantageous. Anita Silvers (1994) gives the example of the great violinist Izhak Perlman, who walks with great difficulty yet has had a life of magnificent artistic accomplishment. However, it is surely to Perlman's disadvantage to have difficulty walking, as Bonnie Steinbock (2000) notes. A particular condition may be disadvantageous even for someone who is fortunate overall.

In light of these definitions impairments may disable a person to different degrees or in different ways in different societies, depending not only on the technology available (as with severe myopia) but more generally on the modes of living prevalent in the person's society, for example, whether the society is literate, whether it is agrarian or industrial, and the forms of transportation available in it. People with impairments also may confront varied cultural obstacles. In a society in which those born with bodily defects are regarded as cursed by the gods, for example, people with congenital impairments may be shunned, barred from most vocations, and reduced to begging. For a less extreme example, in a society in which attendant care is available only to those who live in institutions people who need the help of an aide to dress or bathe must be institutionalized. Someone with the same impairment might live in his or her own home in a different society. Consequently, some have argued that disability is purely a social construct. The degree of disability may indeed vary greatly as a result of cultural factors, however, as defined here, the impairment that causes disability is not fundamentally social in nature.

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