American race law rests on a piece of arithmetic no mathematician would sign: one drop of Black blood makes a person Black, and a flood of white blood makes nobody white. The formula runs in a single direction, and it has run that way for more than three centuries. Ask why the obverse rule never existed, why no statute, no census, no courtroom ever held that a drop of white blood confers whiteness, and you have asked the question that unlocks the whole machinery, because a rule that only works one way was never measuring what it claimed to measure.

Continue reading → The One-Way Drop: Why a Drop of White Blood Never Made Anyone White