Income
The word “income” appears in the Sixteenth Amendment, throughout the Internal Revenue Code, and in hundreds of court opinions — but it has never received a stable, comprehensive definition from any of these sources. This is not a conspiracy; it is a genuine doctrinal gap that creates real interpretive problems.
Eisner v. Macomber (1920) attempted a definition: income is “the gain derived from capital, from labor, or from both combined.” This formulation was narrow enough to exclude stock dividends (the holding of the case) and broad enough to capture wages and investment returns. But it left open the question of what constitutes “gain” — a question that labor-as-exchange theorists have pressed for decades.
Commissioner v. Glenshaw Glass Co. (1955) widened the definition to include “undeniable accessions to wealth, clearly realized, and over which the taxpayers have complete dominion.” Whether this expansion is consistent with the original constitutional meaning of “income” remains a live academic question, even though courts treat it as settled.
The concept page is not an argument. It is a map of the term’s boundaries, contested edges, and the specific cases that drew them.