Under Swedish tax law; the general clause in the Tax Avoidance Act is a method to prevent tax evasion. The purpose of the general clause is to prevent any tax avoidance procedures that the legislator has not been able to foresee. For the general clause to be applicable, four prerequisites need to be met. This thesis analyses the fourth prerequisite based on the principle of legality. The prerequisite concludes that a determination of the tax base, based on the procedure in question, is in conflict with the purpose of the legislation. The prerequisite has been criticized for being difficult to apply. As tax laws are applied beyond the scope of the legislation, it has also been considered that taxation is made without statutory basis, which is conflicting with the principle of legality.

The principle of legality requires the application of law to be predictable and without arbitrary. Therefore, in order to collect taxes there is a requirement of legal authority. Of this requirement, it has been deduced a prohibition on application by analogy of tax laws. Of relevance to the relation between the fourth prerequisite and the principle of legality is what legal value the principle is considered to have. It has been discussed whether the principle of legality can be codified in the constitution.

It has been found that the principle of legality is expressed in the Instrument of Government. It is not considered to be any controversies between the fourth prerequisite and the principle of legality, as there is a legal authority for the taxation that occurs under the general clause. It is also not considered to be any illicit delegations, as the courts only rule on whether the practice is in contrast to tax legislation purposes, and not legislate. The taxpayer therefore has to take the purpose of the legislation into consideration when measures are taken for tax avoidance purposes.