His first error is the act of rewriting the plain text of a law, instead of practicing the disinterested interpretation that is the task of the judiciary, regardless of the partisan outcome. The second error is converting the health insurance mandate's penalty into a tax. Ninety years of precedents have honed precise and widely divergent legal meanings for taxes and penalties for violating laws or regulations, and they are not interchangeable.

The Chief Justice did not simply change a label—as if Congress said something was a penalty when it was really a tax. Rather, these categories are defined by their purposes and effects, by how they operate in practice. Taxes are "exactions" whose main goal is raising revenue, while penalties punish individuals for breaking the law. The boundaries can blur—legitimate taxes may also have strong punitive aims—but scarcely so in this case. ObamaCare's mandate was designed to regulate individual conduct to help achieve universal coverage. If it succeeds perfectly, it should collect $0.