moral character as the key to identity in aeon:

“I inquired what kind of change would render her unrecognisable. My friend responded without hesitation: ‘If she stopped being kind. I would leave her immediately.’ He considered the question a few moments more. ‘And I don’t mean, if she’s in a bad mood or going through a rough time. I’m saying if she turned into a permanent bitch with no explanation. Her soul would be different. This encounter is instructive for a few reasons (not least of which is the intriguing term ‘permanent bitch’) but let’s start with my friend’s invocation of the soul…”