In the United States v. Bishop case of 1972, the U.S Supreme Court had to determine whether a conviction for willful failure to pay taxes required proof that the defendant knew he was breaking a known legal duty. The court held that in tax evasion cases, "willfulness" involves a voluntary and intentional violation of a known legal duty. Therefore, it is not necessary for prosecutors to prove that defendants were aware they were violating specific Internal Revenue Code sections; rather, they must only show that defendants knowingly violated an understood legal obligation not to defraud the government by evading taxes. This ruling clarified previous inconsistencies between different circuit courts regarding what constituted "willfulness" in tax evasion cases.

In the dissenting opinion for United States v. Bishop, Justice Marshall argued that the majority's decision to equate willfulness in tax evasion cases with bad faith or evil intent was too narrow and restrictive. He contended that this interpretation could potentially allow individuals who knowingly violate tax laws to escape punishment if they can convince a court that they did not act out of malice or ill-will. Instead, he proposed a broader definition of willfulness which would include any deliberate and intentional violation of known legal duty, regardless of motive or intent. This approach, he believed, would better serve the purpose of deterring tax evasion by making it clear that any knowing violation is punishable under law.