An argument for assessing decision-making capacity in terms of personal identity, rather than cognitive functioning.
One of the arguments on this score is as follows. The background purpose of the private law is to facilitate flourishing through private ordering. But, as it turns out, people do not generally think that cognitive functioning alone is what matters to whether the law ought to recognize their decision-making. Instead, it seems that what people care about is whether they are, in some meaningful sense, still themselves at the time of a future decision.
In the paper, for support of this proposition, I cite myself — the results of a relatively small study I published here and here that revealed that for study participants, personal identity rather than cognitive functioning was the primary way in which they thought about their legal entitlement to make decisions. But this finding has just received additional empirical support, in the form of a larger experimental study available here as a preprint by Brian Earp, Ivar Hannikainen, Samuel Dale and Stephen Latham.
The study offered participants a prompt drawn from classical debates in bioethics on the ethical status of advance directives — documents composed while at full cognitive abilities that direct certain medical treatment in the event that the author later loses mental capacity.
However, after developing dementia and losing capacity, Robin is described as apparently happy and contended with her life. She develops a disease that will be fatal if untreated, but which is easily treatable. Participants were asked two relevant questions — 1 is Robin with dementia still her true self? And 2 should she be treated? The headline result vindicating the experimental model designed to test advance directive efficacy was that it indeed made a difference for participants whether Robin had completed an advance directive in assessing whether she was still her true self, and whether she should be treated.
