[4th post in a series, start with the first post here]

I’ve been writing this week about Parfit’s idea that personal identity should be thought of as defined by the continuity or overlap in important psychological properties between the self at different times. One question that’s raised by his work is what are important changes in terms of personal identity? Which changes are important enough to disrupt psychological connectedness to the future self, and which changes are merely superficial, not impacting how connected people feel to their future selves?

Nina Strohminger and Shaun Nichols have a fascinating paper looking at mental changes, specifically those caused by dementia, Alzheimers and ALS (Lou Gehrig’s diseases). They study family members of patients suffering from these diseases, looking at relationships with the patient, as well as perceptions of whether the patient is still the same person.

They find that dementia has the strongest negative effect on relationships to family members, and ALS the least, with Alzheimers somewhere in-between.  These differences in negative effects of the diseases on patients’ relatives can be traced back to the relative’s higher perceptions  of the dementia (vs. ALS) patients as a different person.  These perceptions, fundamentally about continuity of others’ identity, in turn, seem to depend most strongly on the relative’s perceptions that the patient’s morality has changed.

To put it another way, the patient’s amnesia, depression, changes in the patient’s personality, and length of illness all had minimal effects on whether the patient’s relatives saw the patient as no longer the same person.  What mattered the most was the relative’s perception of the patient’s morality having changed (as well as, to a lesser degree, the patient having difficulty speaking).  This points to morality as potentially being at the core of what needs to remain the same for people to feel connected to their future selves.

Stephanie Chen, along with Dan Bartels and I, has looked at this same question in a very different way.  She measured people’s causal maps of aspects of their identity (see an example below), by having people identify which aspects of their identity caused which other aspects. She then asked people to identify which aspects, if changed, would be most disruptive to their identity.

She finds that morality is important, but no necessarily the most important, when people are contemplating possible future changes in their own identity.  Instead, what seems to matter the most in this way of looking at it are the causal inter-relationships. Those aspects which are linked to the most other aspects of the self, either as a cause or as an effect, are the ones that are most important for identity.

The aspects that have the most causal connections vary across people.  Of the aspects we tested, the ones that had the most links to other aspects and had the most impact on identity were personal goals and intelligence.  Wholesomeness, loyalty and honesty had somewhat lower levels of both links and perceived impact on identity, on average.

These results suggest that what matters for a person’s identity will depend on how that person sees their personal aspects. If I think of my moral values as connected to lots of others aspects of myself, then I am more likely to see a future change in my morality as disrupting the continuity of my identity. But if I see my moral values as occurring separately from other aspects, then I will tend to see changes in those moral values as less disruptive than something else that is more central and connected — perhaps my intelligence, goals or memories.