 Of course, the MacCAT-T is only one of many instruments that have been developed to assess capacity (Etchells et al. 1999; S. Welie 2001; Vellinga et al. 2004; Dunn et al. 2006; Kim 2010: 61–65) and all such instruments must be assessed for empirical validity, namely the extent to which they successfully track and measure the properties they claim to track and measure. However, questions of empirical validity, though obviously important, are generally of less interest to philosophers. The more interesting questions arise when we consider the adequacy of the underlying theory a particular instrument is based upon. That means that in the case of the MacCAT-T, the deeper, interesting question is whether the four abilities model as specified by Grisso and Appelbaum captures everything important about decision-making capacity. Since to date the four abilities model has been the most influential model by far, the following discussion focuses on it.