 The most basic mental element is understanding (Buchanan &amp; Brock 1989: 23). Obviously, in order to be capable of consenting to or refusing a given intervention, a subject must have some basic understanding of the facts involved in that decision. Yet this apparently simple requirement can turn out to be rather complex depending on how “understanding” itself is defined (Drane 1985). Basic comprehension and knowledge or cognition of facts is one minimal interpretation (Grisso &amp; Appelbaum 1998: 37–42). However, most commentators recognize that this level of mental ability is not enough for generating the sort of medical decisions we are concerned with. On the other hand, the standard cannot be set too high lest we rule too many people incompetent (see inclusivity  §5.1).