Retirement is the point where a person stops employment completely. A person may also semi-retire an keep some sort of retirement job, out of choice rather than necessity. This usually happens upon reaching a determined age, when physical conditions don't allow the person to work any more (by illness or accident), or even for personal choice (usually in the presence of an adequate pension or personal savings). The retirement with a pension is considered a right of the worker in many societies, and hard ideological, social, cultural and political battles have been fought over whether this is a right or not. In many western countries this right is mentioned in national constitutions.