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8 n. 21.

We granted certiorari to consider two questions: (1) whether “critical habitat” under the ESA must also be habitat; and (2) whether a federal court may review an agency decision not to exclude a certain area from critical habitat because of the economic impact of such a designation. 583 U. S. ___ (2018).

Our analysis starts with the phrase “critical habitat.” According to the ordinary understanding of how adjectives work, “critical habitat” must also be “habitat.” Adjectives modify nouns–they pick out a subset of a category that possesses a certain quality. It follows that “critical habitat” is the subset of “habitat” that is “critical” to the conservation of an endangered species.

Of course, “[s]tatutory language cannot be construed in a vacuum,” Sturgeon v. Frost, 577 U. S. ___, ___ (2016) (slip op., at 12) (internal quotation marks omitted), and so we must also consider “critical habitat” in its statutory context. Section 4(a)(3)(A)(i), which the lower courts did not analyze, is the sole source of authority for critical-habitat designations. That provision states that when the Secretary lists a species as endangered he must also “designate any habitat of such species which is then considered to be critical habitat.” 16 U. S. C. §1533(a)(3)(A)(i) (