 Without the mental ability to engage in reasoning and manipulate information rationally, it is impossible for understanding and appreciation to issue in a decision (Buchanan &amp; Brock 1989: 24–25; Grisso &amp; Appelbaum 1998: 52–58). Interestingly, however, the concept of reasoning is often left vague in discussions of decisional capacity. Probably this is because insisting on too high and specific a normative standard of reasoning might risk ruling that a majority of subjects lack capacity, which, again, risks ruling too many people incompetent.