Ability can mean capacity "He has the capacity to do well in school." However, capacity can also mean having authority. "He made a decision in his capacity as mayor." Capacity is also a legal term, meaning the ability to perform some legal act. The term 'diminished capacity' is a legal term meaning a person could not be held legal responsible for their actions because of their confused mental state.

Ability = linear/static Capacity = cross-dimensional/dynamic

Ability is what one is born with; it is dependent upon the genetic makeup of an individual. Capacity is a result of effort and it can be increased through constant exercises and effort whereas ability can be physical or mental. Capacity refers to the potential that an individual can reach in future.It is the maximum limit to which a person or machine can perform without compromising with quality.