There are two contrasting views on the decision-making for life-sustaining treatment in advanced stages of dementia when the patient is deemed incompetent. One is to respect the patient's precedent autonomy by adhering to advance directives or using the substituted judgement standard. The other is to use the best-interests standard, particularly if the current judgement on what is best for the incapacitated patient contradicts the instructions from the patient's precedent autonomy. In this paper, I argue that the protracted clinical course of (...) dementia over many years requires the extended perspective of a progressive decision-making process—extended in both social space and time. The ongoing debate between these two competing views has missed this perspective by focussing on an exclusive disjunction between the competent former self and the incompetent current self. Drawing on theories of situated cognition in cognitive science, I will show that the cognition of a demented patient can be viewed as extended and embodied by her supportive social environment. As the disease progresses, the content of the mind of a demented person becomes partially constituted by such external resources along with her diminishing intrinsic mind. With this understanding, medical decision-making for a demented patient can be construed as a temporally and socially extended practice. A collective decision-making body consisting of the patient, her family and surrogates, and the clinician, should make progressive decisions as a whole over years of the disease course. Finally, I will provide a practical example of how this proposal can be applied in clinical practice. (shrink)