In many Western jurisdictions, the law presumes that adult persons, and sometimes children that meet certain criteria, are capable of making their own health care decisions; for example, consenting to a particular medical treatment, or consenting to participate in a research trial. But what exactly does it mean to say that a subject has or lacks the requisite capacity to decide? This last question has to do with what is commonly called “decisional capacity,” a central concept in health care law and ethics, and increasingly an independent topic of philosophical inquiry.
Decisional capacity can be defined as the ability of health care subjects to make their own health care decisions. Questions of ‘capacity’ sometimes extend to other contexts, such as capacity to stand trial in a court of law, and the ability to make decisions that relate to personal care and finances. However, for the purposes of this discussion, the notion of decisional capacity will be limited to health care contexts only; most notably, those where decisions to consent to or refuse treatment are concerned.
The combined theoretical and practical nature of decisional capacity in the area of consent is probably one of the things that makes it so intellectually compelling to philosophers who write about it. But this is still largely uncultivated philosophical territory. One reason is the highly interdisciplinary and rapidly changing nature of the field. Clinical methods and tests to assess capacity are proliferating. The law is also increasingly being called upon to respond to these clinical developments. All of this makes for a very eclectic and challenging field of inquiry. Philosophers must tread carefully if their contributions are to be timely and relevant.