Sources of Tax Law for Tax Research. What are Primary vs. Secondary authorities? Can you give examples of each? Consider the following sources of tax law: statutes, case law, IRS announcements (i.e., Revenue Rulings, Revenue Procedures, etc.). Which would seem the strongest to you, if any? What about court cases vs. statutes? To what extent does it matter which court the decision comes from, i.e., which courts are more authoritative than others for tax law?