The courts have generally held that direct taxes are restricted to taxes on people (variously called capitation, poll tax or head tax) and property. (Penn Mutual Indemnity Co. v. C.I.R., 227 F.2d 16, 19-20 (3rd Cir. 1960).) All other taxes are known as "indirect taxes," basically tax an event, rather than somebody or property as such. (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 topics th...