Whenever considering a system of categorization, some categories are marked: they’re stated and described. Others can’t be. Some categories are unmarked because they are unknown: this disease hasn’t been witnessed before, we’re still trying to figure out what it is. Still others are unmarked because they’re what the others are a deviation from: consider, there are ten thousand thousand different maladies and diseases in the world; how many kinds of health are there? Consider, also, the Anna Kareinina principle, articulated by Tolstoy: “Happy families are all alike; every unhappy family is unhappy in its own way.”