Today the Supreme Court issued Carr v. United States, and found that “Section 2250 [of SORNA] does not apply to sex offenders whose interstate travel occurred before SORNA’s effective date.” To resolve the meaning of a statute, Justice Sotomayor parsed some grammar and relied on tenses:

The Court instead accepts Carr’s interpre-tation that the statute does not impose liability unless a person, after becoming subject to SORNA’s registration requirements, travelsacross state lines and then fails to register. That interpretation bet-ter accords with §2250(a)’s text, the first element of which can only be satisfied when a person “is required to register under SORNA.” §2250(a)(1). That §2250 sets forth the travel requirement in the pre-sent tense (“travels”) rather than in the past or present perfect (“traveled” or “has traveled”) reinforces this conclusion. See, e.g., United States v. Wilson, 503 U. S. 329, 333. And because the Dic-tionary Act’s provision that statutory “words used in the present tense include the future as well as the present,” 1 U. S. C. §1, implies that the present tense generally does not include the past, regulating a person who “travels” is not readily understood to encompass a per-son whose only travel occurred before the statute took effect. Indeed, there appears to be no instance in which this Court has construed a present-tense verb in a criminal law to reach preenactment conduct. The statutory context also supports a forward-looking construction of “travels.” First, the word “travels” is followed in §2250(a)(2)(B) by aseries of other present tense verbs—“enters or leaves, or resides.” A statute’s “undeviating use of the present tense” is a “striking indic[ator]” of its “prospective orientation.” Gwaltney of Smithfield, Ltd. v. Chesapeake Bay Foundation, Inc., 484 U. S. 49, 59. Second, the other elements of a §2250 violation are similarly set forth in the present tense: Sections 2250(a)(1) and (a)(3) refer, respectively, toany person who “is required to register under [SORNA]” and who “knowingly fails to register or update a registration.” (Emphasis added.) Had Congress intended preenactment conduct to satisfy§2250’s first two requirements but not the third, it presumably wouldhave varied the verb tenses, as it has in numerous other federal stat-utes. Pp. 5–11.

But in dissent, Justice Alito disagrees with Sotomayor’s grammar.

As I read this language, neither the use of the presenttense in paragraph (2)(B) nor the sequence in which the elements are listed provides any basis for limiting the provision to those sex offenders who move from one Stateto another after SORNA’s enactment.

…

Once it is recognized that §2250(a) should not be read asspeaking as of the date when SORNA went into effect, petitioner’s argument about the use of the present tensecollapses. In accordance with current drafting conven-tions, §2250(a) speaks, not as of the time when the law went into effect, but as of the time when the first act necessary for conviction is committed. In the case of §2250(a), that occurs when an individual is convicted of a qualifying sex offense, for it is that act that triggers the requirement to register under SORNA.4 For presentpurposes, we must proceed on the assumption that this event may have occurred before SORNA was enacted.Viewed as of the time when such a pre-SORNA conviction takes place, every subsequent act, including movementfrom State to State, occurs in the future and is thus prop-erly described using the present tense. Accordingly, §2250(a)(2)(B)’s use of the present tense (“travels”) sup-ports the application of the statute to a sex offender, like petitioner, who moved from State to State after convictionbut before SORNA went into effect.5