Social Security considers your work history and education level in addition to your medical situation. The agency's formal definition of illiteracy is the inability to read or write a simple message such as instructions or inventory lists.. By itself, illiteracy does not mean you're disabled. A person unable to read or write can still perform work, even if the work is only simple labor such as housekeeping or roofing. But illiteracy may contribute to disability if you have other ailments and vocational factors are working against you in the job market.