Abstract: 
It is often claimed that (i) disability is bad for disabled people only when they live in an ableist social environment. However, few believe that (ii) having the physical and mental capacities that typify old age is worse than having the capacities of, say, a typical 30 year-old only because we live in an ageist social environment. This is a problem, because it is plausible that (iii) claim (i) is correct if, and only if, claim (ii) also is. The three claims form a trilemma. At least one must be rejected, however attractive each may seem. I submit, first, that how we think about disability-related disadvantage constrains the way we should think of old age-related disadvantages, and vice versa. Second, this constraint forces most of us to revise the way in which we think about either the disadvantages of disability, or old age, or both. Third, ultimately, it is more fruitful to discuss whether the disadvantages specifically connected with disability, or old age, or both, are bad in themselves rather than discussing whether the broad and quite varied set of disadvantages involved in disability and old age, respectively, are bad independently of the nature of the relevant social environment in which they exist.

Key words:
Ageism, disability, disadvantage, age, harm, social model of disability.