Under the benefit principle, taxes are seen as serving a function similar to that of prices in private transactions; that is, they help determine what activities the government will undertake and who will pay for them. If this principle could be implemented, the allocation of resources through the public sector would respond directly to consumer wishes.

In fact, it is difficult to implement the benefit principle for most public services because citizens generally have no inclination to pay for a publicly provided service—such as a police department—unless they can be excluded from the benefits of the service. The benefit principle is utilized most successfully in the financing of roads and highways through levies on motor fuels and road-user fees (tolls). Payroll taxes used to finance social security may also reflect a link between benefits and “contributions,” but this link is commonly weak, because contributions do not go into accounts held for individual contributors.

The requirement that a tax system be efficient arises from the nature of a market economy. Although there are many examples to the contrary, economists generally believe that markets do a fairly good job in making economic decisions about such choices as consumption, production, and financing. Thus, they feel that tax policy should generally refrain from interfering with the market’s allocation of economic resources. That is, taxation should entail a minimum of interference with individual decisions. It should not discriminate in favour of, or against, particular consumption expenditures, particular means of production, particular forms of organization, or particular industries. This does not mean, of course, that major social and economic goals may not take precedence over these considerations. It may be desirable, for example, to impose taxes on pollution as a means of protecting the environment.

Economists have developed techniques to measure the “excess burden” that results when taxes distort economic decision making. The basic notion is that if goods worth $2 are sacrificed because of tax influences in order to produce goods with a value of only $1.80, there is an excess burden of 20 cents. A more nearly neutral tax system would result in less distortion. Thus, an important postwar development in the theory of taxation is that of optimal taxation, the determination of tax policies that will minimize excess burdens. Because it deals with highly stylized mathematical descriptions of economic systems, this theory does not offer easily applied prescriptions for policy, beyond the important insight that distortions do less damage where supply and demand are not highly sensitive to such distortions. Attempts have also been made to incorporate distributional considerations into this theory. They face the difficulty that there is no scientifically correct distribution of income.

In discussing the general principles of taxation, one must not lose sight of the fact that taxes must be administered by an accountable authority. There are four general requirements for the efficient administration of tax laws: clarity, stability (or continuity), cost-effectiveness, and convenience. Administrative considerations are especially important in developing countries, where illiteracy, lack of commercial markets, absence of books of account, and inadequate administrative resources may hinder both compliance and administration. Under such circumstances the achievement of rough justice may be preferable to infeasible fine-tuning in the name of equity.

Tax laws and regulations must be comprehensible to the taxpayer; they must be as simple as possible (given other goals of tax policy) as well as unambiguous and certain—both to the taxpayer and to the tax administrator. While the principle of certainty is better adhered to today than in the time of Adam Smith, and arbitrary administration of taxes has been reduced, every country has tax laws that are far from being generally understood by the public. This not only results in a considerable amount of error but also undermines honesty and respect for the law and tends to discriminate against the ignorant and the poor, who cannot take advantage of the various legal tax-saving opportunities that are available to the educated and the affluent. At times, attempts to achieve equity have created complexity, defeating reform purposes.

Tax laws should be changed seldom, and, when changes are made, they should be carried out in the context of a general and systematic tax reform, with adequate provisions for fair and orderly transition. Frequent changes to tax laws can result in reduced compliance or in behaviour that attempts to compensate for probable future changes in the tax code—such as stockpiling liquor in advance of an increased tariff on alcoholic beverages.

The costs of assessing, collecting, and controlling taxes should be kept to the lowest level consistent with other goals of taxation. This principle is of secondary importance in developed countries, but not in developing countries and countries in transition from socialism, where resources needed for compliance and administration are scarce. Clearly, equity and economic rationality should not be sacrificed for the sake of cost considerations. The costs to be minimized include not only government expenses but also those of the taxpayer and of private fiscal agents such as employers who collect taxes for the government through the withholding procedure.

Payment of taxes should cause taxpayers as little inconvenience as possible, subject to the limitations of higher-ranking tax principles. Governments often allow the payment of large tax liabilities in installments and set generous time limits for completing returns.