-What does this look like for psychological theories? In the crudest form, when we notice a pattern of traits that go together, we give it a name.
+What does this look like for psychological theories? In the crudest form, when we notice a pattern of traits that go together, we give it a name. Sometimes people go through cycles of elevated arousal and hyperactivity, punctuated by pits of depression. After seeing the same distinctive patterns in many such cases, doctors decided to reify it as a diagnosis, ["bipolar disorder"](https://en.wikipedia.org/wiki/Bipolar_disorder).
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+If we notice further patterns _within_ the group of cases that make up a category, we can spit it up into sub-categories: a diagnosis of bipolar I requires a full-blown manic episode, but hypomania and a major depressive episode qualify one for bipolar II.
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+Are bipolar I and bipolar II "really" different conditions?
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