Final answer:
IRS publications are not considered a primary source of tax law compared to judicial decisions, statutes, treaties, and the Constitution.
Step-by-step explanation:
The correct answer is 3) IRS publications, which is not considered a primary source of tax law. Primary sources of tax law include judicial decisions, statutes, treaties, and the Constitution.
Judicial decisions refer to the rulings made by courts in tax cases, which help establish legal precedent. Statutes are laws enacted by legislative bodies, such as Congress, that outline the rules and regulations governing taxation. Treaties are international agreements between countries that address tax-related matters. The Constitution serves as the supreme law of the land and establishes the framework for the government's authority to levy taxes.