The Wealth of Nations by Part 5 Chapter 2 Page 164

rigorously exacted, afford a very sure revenue to the state. It is upon this account that in countries where the ease, comfort, and security of the inferior ranks of people are little attended to, capitation taxes are very common. It is in general, however, but a small part of the public revenue which, in a great empire, has ever been drawn from such taxes, and the greatest sum which they have ever afforded might always have been found in some other way much more convenient to the people.

Taxes upon Consumable Commodities

The impossibility of taxing the people, in proportion to their revenue, by any capitation, seems to have given occasion to the invention of taxes upon consumable commodities. The state, not knowing how to tax, directly and proportionably, the revenue of its subjects,