According to the IRS’s own Tax Crimes Handbook, there are three elements to the criminal offense evasion of assessment —commonly called “tax evasion.” It requires that: (1) the taxpayer “attempt to evade or defeat a tax or the payment of a tax,” (2) there be an additional tax due and owing; and (3) the taxpayer acted “willfully” in his actions to evade the tax. (The corresponding Internal Revenue Code Section for tax evasion is IRC 7201). Each of these elements must be proved “beyond a reasonable doubt.”
The key part of this crime is the first requirement—that the taxpayer “attempt” to evade the tax. There are several ways this element may be satisfied. However, at a broad level, what is required is that the taxpayer engage in “some affirmative action of attempting to evade or defeat” the tax, as the Handbook puts it.