-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". The simple high-level category ("bipolar disorder") is a useful approximation, in the absence of knowing the sub-category (bipolar I _vs._ II) and the subcategory is a useful approximation in the absence of knowing the patient's detailed case history.
+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". The simple high-level category ("bipolar disorder") is a useful approximation in the absence of knowing the sub-category (bipolar I _vs._ II), and the subcategory is a useful approximation in the absence of knowing the patient's detailed case history.