Let us begin this answer with an anecdote from which one of my academic sources takes its title:
During the 1980 Olympic games in Moscow, a Western journalist inquired whether the Soviet Union would participate in the first Paralympic games, scheduled to take place in Great Britain later that year.
The reply from a Soviet representative was swift, firm, and puzzling: "There are no invalids in the USSR!"
In other words, just a handful of years before the dissolution of the USSR, on the dawn of the Paralympics for people with physical disabilities (and more than a decade after Eunice Kennedy Shriver founded the Special Olympics for people with intellectual disabilities), the official Soviet line was unequivocal: there were simply no disabled people in the USSR.
Of course, we know that this is impossible. However, that anecdote helps illustrate some of the public attitudes towards disability in the USSR.
Legally, disabled people were defined as invalidnost, or people who had lost the ability to work. Formally, invalidnost are described in law in the 1956 Law on State Pensions, where disability is legally defined as "a loss of labor capacity." As you might imagine, this was not smiled upon in a society where the law also dictated that citizens were required to engage in paid labor as a "socially useful activity."
Phillips (2009) notes some of the philosophy concerning disability:
The Soviet state's approach to disability was not really the "individual, tragic" model found in the U.S., Great Britain, and elsewhere and so criticized by disability rights advocates beginning in the 1960s. Rather, the Soviet state employed a functional model of disability, based on a person's perceived "usefulness for society."
As early as 1932, the USSR set about formally describing the three categories of disabled people:
Group I includes those considered unable to work and deemed to require constant nursing care; group II includes those not perceived to require constant nursing care who have lost some capability to work but may work in special conditions; people in group III are considered the partially disabled who have lost some work capability but may engage in part-time or casual work.
Group I individuals would have been cared for by the state, likely in group home settings not unlike an adult nursing home or orphanage. Group II and Group III people would be assigned to whatever workload the state felt they were capable of doing. In the event of physical injury like an amputation from an industrial accident, a work could be reassigned to adapted duties.
As for mental illness, the USSR banned lobotomies in 1950 (despite them being quite in vogue in the West at the time as a treatment for a variety of mental illnesses.) They did, however, institutionalize the severely mentally ill:
Chlorpromazine... was first used in Moscow in 1954 and was officially approved in 1955. Unlike in the West, however, the new psychopharmaceuticals did not lead to deinstitutionalisation. I argue that the new drugs did not disrupt the existing Soviet system because... the Soviets were already dedicated, at least in theory, to a model which paired psychiatric hospitals with community-based 'neuropsychiatric dispensaries.'
The main consideration for disability in the USSR was ability to work. If you could still work, you had social value; if you could not work, you were running afoul of a system predicated on the individual being understood as a worker first. It's worth noting that since many Soviet citizens were assigned work based on capacity or need (not their choice), the state would assess their utility and simply assign them to work the person appeared to be capable of doing.
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