Capacity to consent to or refuse treatment and/or research: theoretical considerations.

This article discusses theoretical dimensions of competency to consent to or refuse treatment and/or research. We will consider a number of issues. Our first subject is the nature of assessments of competency-their empirical, normative, and conceptual aspects. We then discuss how we should divide up the components of capacity-understanding, appreciation, reasoning, and evidencing a choice; how we should understand these different components; and whether all are indeed necessary. We discuss where to draw the line between capacity and incapacity on each of the four elements of capacity. We ask whether we should have a variable competency standard, either in general or in different contexts (e.g. treatment versus research). Finally we consider the role of mental illness in competency assessments.