2.2 Principles of Taxation Law

1. Legality — no tax without legislation (Article 115's principle: no tax except by law). 2. Ability to pay — equity's legal echo. 3. Certainty and prospectivity — a tax law speaks from its commencement; retroactive taxation is exceptional and must be express. 4. Equality before the tax law — Article 18's equal protection extends to taxpayers. 5. Strict construction — charging provisions are read strictly; ambiguity in the taxpayer's favour (the contra fiscum tendency), while relief provisions are read as written. 6. Due process — notice, hearing, reasons, appeal (the administrative-law guarantees, LAW5605). 7. No discrimination without classification's reason — classifications among taxpayers must bear a rational nexus to the tax's purpose.