Direct-Tax
Brushaber held the income tax is an excise, not a direct tax
Brushaber v. Union Pacific (1916) characterized the income tax as an excise. This characterization is correct, underappreciated, and load-bearing for understanding what the Sixteenth Amendment did and didn't do.
Pollock was never overruled — only circumvented by the Sixteenth Amendment
Pollock v. Farmers' Loan (1895) remains technically good law. The Sixteenth Amendment routed around it without overruling it. This is doctrinally true and partially load-bearing.
Pollock v. Farmers' Loan & Trust Co.
Struck down the 1894 income tax as a direct tax on income from property requiring apportionment among the states.
Apportionment
The constitutional requirement that direct taxes be allocated among the states by population. The mechanism the Sixteenth Amendment removed for income taxation.
Direct Tax
A tax on the ownership of property as such, requiring apportionment among the states by population under Art. I §§2 and 9 of the Constitution.