In addition to its connection to the Simple View, a broader methodological connection unites haecceitism and inquiries into personal identity: a focus on the qualitative/non-qualitative distinction. In debates about personal identity, appeal to exclusively qualitative properties and relations (e.g., having such-and-such psychological features) rather than non-qualitative properties and relations (e.g., having Bob’s memories) is commonly taken as a constraint on a genuinely reductive analysis of personal identity over time. So, just as haecceitism requires clarifying the nature of this metaphysical distinction, criteria for distinguishing the reductive and non-reductive approaches to personal identity also rely heavily on the idea that certain properties are uniquely tied to the identity of individuals. On the connection between haecceitism, the Simple View, and (anti-)reductionist approaches to personal identity, see Ninan (2009).