 A third assumption that pervades contemporary work on decisional capacity is that for practical purposes, a ruling on capacity must be all-or-nothing: either the patient in question has decisional capacity or she lacks it. Of course, in many contexts there is an obvious sense in which we can speak meaningfully of “degrees” of capacity, for we are indeed measuring abilities that fall along a spectrum. However, in practice we need a judgment of a bivalent type. This is because we need to know who has final decision-making authority and there is no such thing as “sort of” having authority over a decision. If a patient has the capacity to make decision X, then others must honor her choice even if they disagree with it. But if she lacks capacity to make decision X, someone else, a guardian or surrogate will have to decide for her. To avoid potentially endless controversy and ensure the smooth operation of the healthcare system, law and practice need a “yes-or-no” verdict about whether a person can make a particular decision for herself or not (Buchanan &amp; Brock 1989: 27).