Capability and competency are two words that are often used in business sectors, such as Human resources. They are also used for communications between employees. Capability is a word to describe someone being capable of an action or a requirement. The person is able to learn or do something in their capacity. It could be skills that they already have or skills that they can learn.
Competency is used to describe the state of the work that a person has done. It evaluates their capabilities and if it is deemed positive, the competency could lead to more work or responsibilities.
Capability is the ability to do something. It may refer to a person’s capacity to pay for a few things. For example, you may say that someone is capable of purchasing her own house because she has enough funds to do so.
When you also say that someone is capable, this also means that a person will be able to do something if he/she would like to. When you refer to competency, this means that a person is competent or can be trusted to do some things that people will not be able to do.
There are some people who are more competent than others precisely because they are more skilled or they have acquired more knowledge about something.