Editor’s note (June 20th 2024): The Supreme Court has ruled in Moore v United States, upholding the tax at issue (the “mandatory repatriation tax”). The court declined to weigh in on the constitutionality of a tax on unrealised gains.

What is income, really? Ask an economist and they might describe “Haig-Simons” income—the value of a person’s consumption of goods and services, plus the change in their net worth over a certain period. A lawyer might refer to Section 61(a) of the IRS Code 26, which defines “gross” income as “all income from whatever source derived”, including but not limited to commission, interest, property deals and wages. An accountant might talk about how to reduce that gross income, via deductions or carve-outs, to a skinnier “taxable income base”.