In theory, a competent patient may refuse any and all treatments, even those that sustain life. The problem with this theory, confidently and frequently asserted, is that the circumstances of real patients may so confound us with their complexity as to shake our confident assumptions to their core.For instance, it is not the case that one may always and easily know which patients are competent. Indeed, evaluation of decision-making capacity is notoriously difficult. Not only may reasonable and experienced evaluators, say (...) a judge and a psychiatrist, disagree, but also a person's capacity may change from hour to hour and may extend to some decisions yet not to others. And yet it is on this subtle art of capacity evaluation that life and death decisions often turn, especially when patients decline life-sustaining treatment.An evaluation of capacity may consider the impact of serious medical or psychiatric illness, as well as the patient's life circumstances. (shrink)