The proper interpretation of the legal provisions in the field of tax law has high importance because it determines the opportunities of the taxpayers.  Taxpayers normally wish to pay as little tax as possible, in contrast, the tax authorities try to collect as much tax as, according to them, is still lawful. If a taxpayer makes an error in his legal interpretation, he has to face the legal consequences, that is why it is necessary to know the case law. In the English law and in the law of the United States, two fundamental approaches of the interpretation of tax law have emerged: according to the strict approach, the judicature has to scrutinize only the meaning of the words of the act and that is what determines the question of the tax burden. On the other hand, the other approach means that the purpose of the questionable transaction or the intention of the legislator shall be taken into consideration as well, but only in that case in which the application of the words would lead to an unreasonable result. This paper analyzes the relevant precedents of the United States, mentioning many examples and scrutinizes the theoretical bases and the application of the two approaches mentioned.