Changes in the environment and in the functioning of the older person can lead to the deterioration of the ability to control that environment. Problematical behaviour in the third life phase can partly be seen as a strategy to restore this deminishing control over the environment. In consequence of this, depression, hypochondria and paranoia in particular tend to have a different colouring in the third life phase than they have in previous phases. The process of dementia is possibly accelerated either through the (unsuccessful) effort of the demented person to re-establish control over the environment or just by giving up all efforts to re-establish this control.