The topic of discussion for this Constitution Monday comes from Article I, Section 9, Clause 4: "No Capitation, or other direct, Tax shall be laid, [unless in Proportion to the Census or enumeration herein before directed to be taken.]" This principle of the United States Constitution guaranteed to American citizens that they would never be subject to a fixed tax of so much per person except in proportion to the population of their state.
"The word capitation comes from a Latin word meaning `head.' Therefore, any reference to capitation taxes or poll taxes refers to a tax which is levied at `so much per head,' regardless of circumstance. The Founders were well aware that this is not a fair tax, but it is the most easily collected in an emergency. But how much should the head tax be? Should this be determined by the wealth of the state, or its population? … [T]he Founders felt there was no way of accurately determining the wealth of a state, whereas there could be no question as to the number of people. For this reason they concluded at the Convention to make it a matter of constitutional mandate that if the government was ever forced to levy a head tax on the states, it would be according to the population." (See W. Cleon Skousen in The Making of America - The Substance and Meaning of the Constitution, p 477.)
Due to the fact that the Articles of Confederation did not give the national government much power to raise revenue, the Founders wanted to give the federal government more power to do so even though they were very concerned about taxes. "Indirect taxes (generally understood as falling on articles of consumption) did not lend themselves to congressional abuse …, but the Framers believed that `directed taxes' needed to be cabined. The cumbersome apportionment rule, requiring that a direct tax be apportioned among the states on the basis of population (so that, for example, a state with twice the population of another state would have to pay twice the tax, even if the more populous state's share of the national tax base were smaller), made the more dangerous taxes politically difficult for Congress to impose….
"Direct taxes, which were expected to be used only in emergencies, did not have the built-in protections characteristic of indirect taxes. Direct taxes were imposed directly on individuals, who, it was assumed, could not shift their liability to others. If a tax was not indirect, the Framers though it should be apportioned. Capitation and land taxes were direct under this understanding, but so might other taxes be whether known in 1787 or not. If nothing else, a broader understanding of `direct taxes' should require that the constitutional character of any proposed tax be studied before it is enacted in an unapportioned form." (See Erik M. Jensen in The Heritage Guide to the Constitution, pp 159-160.)