Tax: discrimination: petitioner (CSX) is an interstate rail carrier that operates, and pays taxes, in Alabama. The State imposes sales and use taxes on railroads when they purchase or consume diesel fuel, but exempts their main competitors—interstate motor and water carriers. CSX sued respondents, the Alabama Department of Revenue and its Commissioner (Alabama), claiming that this tax scheme discriminates against railroads in violation of the Railroad Revitalization and Regulatory Reform Act of 1976; CSX may challenge Alabama’s sales and use taxes under §11501(b)(4); the key question thus becomes whether a tax might be said to “discriminate” against a railroad under subsection (b)(4) where the State has granted exemptions from the tax to other entities (here, the railroad’s competitors); to say that such a tax does not “discriminate” is to adopt a definition at odds with the word’s natural meaning. This Court has repeatedly recognized that tax schemes with exemptions may be discriminatory. See, e.g., Davis v. Michigan Department of Treasury, 489 U. S. 803; Subsections (b)(1)–(3) specifically allow property tax exemptions, but neither they nor any other provision of the Act speaks to non-property exemptions like those at issue here (U.S.S.Ct., 22.02.11, CSX Transportation v. Alabama, J. Kagan).