Disability can be based on a work related or non-work related injury or illness, be it physical, emotional, or a combination. In order to be disabled by social security regulations, you have to prove that you cannot do any of your past relevant work (work you have done in the past 15 years as well as any other sufficient jobs available in the national economy of the United States).
Basically, there are three ways in which the social security administration will consider you to be disabled; 1) Application of the listings of impairments, 2) Application of the “Grid”, 3) Erosion (elimination) of the sedentary work basis.
The first way to attest your disability is by proving that your condition meets or equals at least one of the Social Security listings of impairments. You can find the listings here: http://www.ssa.gov/disability/professionals/bluebook/AdultListings.htm.
As the term implies, the Social Security administration has created a list of medical impairments that cover multiple medical conditions which affect both physical and mental abilities. If your condition meets or equals all of the requirements of a specific listing, you will be considered disabled as a matter of law. The bad news, however, is that most claimants do not meet or equal all of the listings. As you can see by reviewing the above link, not only do you have to suffer from a condition described in the listings, you also have to meet every single specification contained under the listing upon which your medical condition falls. If you do not meet or equal every single requirement, you do not meet the listing at all.
The second way in which you can be considered disabled is by way of the Medical-Vocational Guidelines, also known as “the Grid”. In order to determine whether you are disabled, Social Security considers your physical and mental ability to work taking into account your medical impairments, age, education and previous work experience. Social Security has arranged these categories in the form of a grid. You can review the Grid here: http://www.ssa.gov/OP_Home/cfr20/404/404-ap11.htm.
In order to take advantage of the Grid, one has to prove that the skills acquired (if any) while doing past relevant work are not transferable to physically lighter work. Unfortunately, many claims are denied by way of the Grid because younger individuals that cannot do any of their past relevant work can still perform a physically lighter job.
It is important to note, though, that if your claim is based mainly on mental/psychological impairments, the Grid is not applicable.
The third way to prove disability is by showing that your ability to a sit-down job (or one where sitting is or can be done the majority of the work day) has been significantly eliminated. This type of work is referred to as sedentary work, defined as a situation where “an individual must have the ability to lift no more than 10 pounds at a time and occasionally to lift or carry articles like docket files, ledgers, and small tools”.
Significant limitations in the use of the hands and eye-sight could also eliminate sedentary job positions. The same is true with significant mental restrictions that cause a substantial loss in the ability to meet any one of several basic work-related activities on a sustained basis.