-[In the case of male-to-female transsexualism, straight and gay trans women seem different. Many authors agree to this simple story! e.g., Veale, Vitale, possibly Serano 2020 —but they have different detailed theories as to how the two clusters come about—the simple story is a useful approximation even if you don't know how to pin down the more detailed story]
+Is the two-type typology of bipolar disorder a good theory? Are bipolar I and bipolar II "really" different conditions, or slightly different presentations of "the same" condition, part of a "bipolar spectrum" along with cyclothymia? In our current state of knowledge, this is debateable! But if our understanding of the etiology of bipolar disorder were to advance, and we were to find evidence that that bipolar I has a different underlying _causal structure_ from bipolar II (with decision-relevant consequences, like responding to different treatments), that would support a policy of thinking and talking about them as mostly separate things (even while they have enough in common to both be kinds of "bipolar").