The 18th-century philosopher Adam Smith attempted to systematize the rules that should govern a rational system of taxation. In his books he set down three general canons.
I. The subjects of every state ought to contribute towards the support of the government in proportion to their respective abilities, that is, in proportion to the revenue which they respectively enjoy under the protection of the state.
II. The tax which each individual is bound to pay ought to be certain, and not arbitrary. The time of payment, the manner of payment, the quantity to be paid, ought all to be clear and plain the contributor, and to every other person.
III. Every tax might to be levied at the time, or in the manner, in which it is most likely to be convenient for the contributor to pay it. Although they need to be reinterpreted from time to time, these principles, especially the first, retain remarkable relevance. From the first can be derived both of the leading views of what is fair in the distribution of tax burdens among taxpayers. These are the belief that taxes should be based on the individual's ability to pay, known as the ability-to-pay principle, and the benefit principle, the idea that there should be some equivalence between what the individual pays and the benefits he derives from governmental activities.
