The courts have generally held that direct taxes are limited to taxes on people (variously called capitation, poll tax or head tax) and property. (Penn Mutual Indemnity Denver. v. C.I.R., 227 F.2d 16, 19-20 (3rd Cir. 1960).) All the other taxes are known as "indirect taxes," because they tax an event, rather than person or property per se. (Steward Machine Co. v. Davis, 301 U.S. 548, 581-582 (1937).) What got a straightforward limitation on the power of the legislature based on the main topi...