Disability refers to the social effects of physical or mental impairment. This definition, known as the 'social model' of disability, makes a clear distinction between the impairment itself (such as a medical condition that makes a person unable to walk or unable to sit) and the disabling effects of society in relation to that impairment. As Frank Bowe put it in Handicapping America (1978), the real issue is the societal response to disability: if a community allows physical, architectural, transportation, and other barriers to remain in place, society is creating handicaps that oppress individuals with disabilities. If, on the other hand, a community removes those barriers, persons with disabilities can function at much higher levels. In simple terms, it is not the inability to walk or inability to sit that prevents a person entering a building unaided but the existence of stairs or the lack of benches to lie down, that are inaccessible to a wheelchair-user or a person with sitting disability. In other words, 'disability' is socially constructed. The 'social model' is often contrasted with the 'medical model' which sees 'disability' as synonymous with 'impairment.'