Article 47 establishes a strict legal constraint on the granting of tax exemptions. It states that no income subject to tax under the provisions of the Income Tax Law may be exempted unless such an exemption is explicitly granted by virtue of a Royal Decree or another Law. This provision prevents the arbitrary granting of tax relief by administrative bodies and ensures that all tax exemptions are rooted in high-level legislative authority, maintaining the integrity and universality of the tax system in Oman.