[Paracompact]

Most disorders in the DSM-5 are defined by polythetic criteria, i.e. meeting X out of Y symptoms from a list for a given duration of time, or by conjunction of polythetic criteria. These definitions are socially constructed and statistically validated for pragmatic use, but very rarely have definite underlying biological markers. Especially as concerns personality disorders, these disorders can also simply be an inheritance of cultural or political baggage and prior psychoanalytic theory.

> In some circumstances the only way to tell the difference between the two is what drugs work: if antidepressants help, it's Major Depression; if mood stabilizers help, it's Bipolar Depression.

This is ridiculous. There is zero mention in the DSM-5 or ICD-11 of "if these drugs work, it's this, otherwise it's this." I would question a psychiatrist dispositively making a diagnosis on such grounds.