Dementia is the progressive decline in cognitive function due to damage or disease in the body beyond what might be expected from normal aging. Dementia persons cannot reasonably live their lives. In order to support dementia persons' lives, various approaches are proposed. Bozeat and Hodges showed affordance might give a certain support to (semantic) dementia persons of understanding (meanings of) objects. In this paper, based on the concept of affordance, abduction, and chance discovery, a dementia care under the concept of affordance is proposed.