opinion: Justice Stevens
  delivered the opinion of the Court.
  The United States Court of Appeals for the Fifth Circuit declared unconstitutional two sections of a licensing ordinance governing coin-operated amusement establishments in the city of Mesquite, Texas. Section 6 of Ordinance 1353, which directs the Chief of Police to consider whether a license applicant has any “connections with criminal elements,” was held to be unconstitutionally vague. Section 5, which prohibits a licensee from allowing children under 17 years of age to operate the amusement devices unless accompanied by a parent or legal guardian, was held to be without a rational basis. The first holding rests solely on the Due Process Clause of the Fourteenth Amendment to the United States Constitution. The Court of Appeals stated that its second holding rested on two provisions of the Texas Constitution as well as the Fourteenth Amendment to the Federal Constitution. Because Congress has limited our jurisdiction to review questions of state law, and because there is ambiguity in the Court of Appeals’ second holding, we conclude that a remand for clarification of that holding is necessary. There is, however, no impediment to our review of the first holding.
  On April 5, 1976, to accommodate the proposal of Aladdin’s Castle, Inc. (Aladdin), to open an amusement center in a shopping mall, the city exempted from the prohibition against operation of amusement devices by unattended children certain amusement centers, the features of which were defined in terms of Aladdin’s rules, as long as children under the age of seven were accompanied by an adult. Thereafter, Aladdin entered into a long-term lease and made other arrangements to open a center in the mall. In August, however, its application for a license was refused because the Chief of Police had concluded that Aladdin’s parent corporation was connected with criminal elements. Aladdin then brought suit in a Texas state court and obtained an injunction requiring the city to issue it a license forthwith. The Texas court found that neither Aladdin nor its parent corporation had any connection with criminal elements and that#he vagueness in the ordinance contravened both the Texas and the Federal Constitutions.
  On February 7, 1977, less than a month after the city had complied with the state-court injunction by issuing the license to Aladdin, the city adopted a new ordinance repealing Aladdin’s exemption, thereby reinstating the 17-year age requirement, and defining the term “connections with criminal elements” in some detail. Aladdin then commenced this action in the United States District Court for the Northern District of Texas, praying for an injunction against enforcement of the new ordinance. After a trial, the District Court held that the language “connections with criminal elements,” even as defined, was unconstitutionally vague, but the District Court upheld the age restriction in the ordinance. As already noted, the Court of Appeals affirmed the former holding and reversed the latter.
  Invoking our appellate jurisdiction under 28 U. S. C. § 1254(2), the city now asks us to reverse the judgment of the Court of Appeals. After we noted probable jurisdiction, 451 U. S. 981, Aladdin advised us that the ordinance reviewed by the Court of Appeals had been further amended in December 1977 by eliminating the phrase “connections with criminal elements.” The age restriction, however, was retained.
  I
  A question of mootness is raised by the revision of the ordinance that became effective while the case was pending in the Court of Appeals. When that court decided that the term “connections with criminal elements” was unconstitutionally vague, that language was no longer a part of the ordinance. Arguably, if the court had been fully advised, it would have regarded the vagueness issue as moot. It is clear to us, however, that it was under no duty to do so.
  It is well settled that a defendant’s voluntary cessation of a challenged practice does not deprive a federal court of its power to determine the legality of the practice. Such abandonment is an important factor bearing on the question whether a court should exercise its power to enjoin the defendant from renewing the practice, but that is a matter relating to the exercise rather than the existence of judicial power. In this case the city’s repeal of the objectionable language would not preclude it from reenacting precisely the same provision if the District Court’s judgment were vacated. The city followed that course with respect to the age restriction, which was first reduced for Aladdin from 17 to 7 and then, in obvious response to the state court’s judgment, the exemption was eliminated. There is no certainty that a similar course would not be pursued if its most recent amendment were effective to defeat federal jurisdiction. We therefore must confront the merits of the vagueness holding.
  “It is a basic principle of due process that an enactment is void for vagueness if its prohibitions are not clearly defined.” Grayned v. City of Rockford, 408 U. S. 104, 108 (emphasis added). We may assume that the definition of “connections with criminal elements” in the city’s ordinance is so vague that a defendant could not be convicted of the offense of having such a connection; we may even assume, without deciding, that such a standard is also too vague to support the denial of an application for a license to operate an amusement center. These assumptions are not sufficient, however, to support a holding that this ordinance is invalid.
  After receiving recommendations from the Chief of Police, the Chief Building Inspector, and the City Planner, the City Manager decides whether to approve the application for a license; if he disapproves, he must note his reasons in writing. The applicant may appeal to the City Council. If the City Manager disapproved the application because of the Chief of Police’s adverse recommendation as to the applicant’s character, then the applicant must show to the City Council that “he or it is of good character as a law abiding citizen,” which is defined in the ordinance to “mean substantially that standard employed by the Supreme Court of the State of Texas in the licensing of attorneys as set forth in [the Texas statutes].” § 9 of Ordinance 1353, App. to Juris. Statement 13. An applicant may further appeal to the state district court. It is clear from this summary that the phrase “connections with criminal elements,” as used in this ordinance, is not the standard for approval or disapproval of the application.
  The applicant’s possible connection with criminal elements is merely a subject that the ordinance directs the Chief of Police to investigate before he makes a recommendation to the City Manager either to grant or to deny a pending application. The Federal Constitution does not preclude a city from giving vague or ambiguous directions to officials who are authorized to make investigations and recommendations. There would be no constitutional objection to an ordinance that merely required an administrative official to review “all relevant information” or “to make such investigation as he deems appropriate” before formulating a recommendation. The judgment of the Court of Appeals was therefore incorrect insofar as it held that the directive to the Chief of Police is unconstitutionally vague.
  II
  The Court of Appeals stated that its conclusion that the age requirement in the ordinance is invalid rested on its interpretation of the Texas Constitution as well as the Federal Constitution:
  “We hold that the seventeen year old age requirement violates both the United States and Texas constitutional guarantees of due process of law, and that the application of this age requirement to coin-operated amusement centers violates the federal and Texas constitutional guarantees of equal protection of the law.” 630 F. 2d 1029, 1038-1039 (1980) (footnotes omitted).
  In the omitted footnotes the court quoted two provisions of the Texas Constitution that are similar, but by no means identical, to parts of the Federal Constitution.
  Because our jurisdiction of this appeal is based on 28 U. S. C. §1254(2), we are precluded from reviewing the Court of Appeals’ interpretation of the Texas Constitution. For the federal statute provides:
  “Cases in the courts of appeals may be reviewed by the Supreme Court by the following methods:
  “(2) By appeal by a party relying on a State statute held by a court of appeals to be invalid as repugnant to the Constitution, treaties or laws of the United States, but such appeal shall preclude review by writ of certio-rari at the instance of such appellant, and the review on appeal shall be restricted to the Federal questions presented . . . .”
  If the Texas Constitution provides an independent ground for the Court of Appeals’ judgment, our possible disagreement with its exposition of federal law would not provide a sufficient basis for reversing its judgment. If that be so, we should simply dismiss the appeal insofar as the city seeks review of the invalidation of the age requirement. Cf. United States v. Hastings, 296 U. S. 188, 193.
  The city contends, however, that the Court of Appeals did not place independent reliance on Texas law but merely treated the Texas constitutional protections as congruent with the corresponding federal provisions. Under this reading of the Court of Appeals’ opinion, our correction of any federal error automatically would result in a revision of the Court of Appeals’ interpretation of the Texas Constitution. Instead of providing independent support for the judgment below, the Texas law, as understood by the Court of Appeals, would be dependent on our reading of federal law. Although the city’s contention derives support from the Court of Appeals’ greater reliance on federal precedents than on Texas cases, we nevertheless decline, for the reasons that follow, to decide the federal constitutional question now.
  It is first noteworthy that the language of the Texas constitutional provision is different from, and arguably significantly broader than, the language of the corresponding federal provisions. As a number of recent State Supreme Court decisions demonstrate, a state court is entirely free to read its own State’s constitution more broadly than this Court reads the Federal Constitution, or to reject the mode of analysis used by this Court in favor of a different analysis of its corresponding constitutional guarantee. See generally Brennan, State Constitutions and the Protection of Individual Rights, 90 Harv. L. Rev. 489 (1977), and cases cited therein. Because learned members of the Texas Bar sit on the Court of Appeals for the Fifth Circuit, and because that court confronts questions of Texas law in the regular course of its judicial business, that court is in a better position than are we to recognize any special nuances of state law. The fact that the Court of Appeals cited only four Texas cases is an insufficient basis for concluding that it did not make an independent analysis of Texas law.
  Second, it is important to take note of the Court of Appeals’ interpretation of the Texas “requirement of legislative rationality.” That interpretation seems to adopt a standard requiring that a legislative classification rests “ ‘ “upon some ground of difference having a fair and substantial relation to the object of the legislation . . . 630 F. 2d, at 1039. This formulation is derived from this Court’s opinion in F. S. Royster Guano Co. v. Virginia, 253 U. S. 412, 415. But it is unclear whether this Court would apply the Royster Guano standard to the present case. See United States Railroad Retirement Bd. v. Fritz, 449 U. S. 166; Craig v. Boren, 429 U. S. 190. Therefore, it is surely not evident that the Texas standard and the federal standard are congruent.
  Finally, and of greater importance, is this Court’s policy of avoiding the unnecessary adjudication of federal constitutional questions. As we recently have noted, see Minnick v. California Dept. of Corrections, 452 U. S. 105, this self-imposed limitation on the exercise of this Court’s jurisdiction has an importance to the institution that transcends the significance of particular controversies. No reason for hasty decision of the constitutional question presented by this case has been advanced. If Texas law provides independent support for the Court of Appeals’ judgment, there is no need for decision of the federal issue. On the other hand, if the city is correct in suggesting that the Court of Appeals’ interpretation of state law is dependent on its federal analysis, that court can so advise us and we can then discharge our responsibilities free of concern that we may be unnecessarily reaching out to decide a novel constitutional question.
  The judgment of the Court of Appeals is reversed in part, and the case is remanded for further proceedings consistent with this opinion.
  It is so ordered.
  630 F. 2d 1029 (1980).
  Section 6 of Ordinance 1353 of the Code of the city of Mesquite provided in pertinent part:
  “Any person desiring to obtain a license for a coin-operated amusement establishment shall apply to the City Secretary by original and five (5) copies, one of which shall be routed to the City Manager, Chief of Police, Chief Building Inspector and City Planner, for review.
  “Upon approval by each of the parties and payment of the license fee, the City Secretary shall issue a license for such establishment, which shall be valid for one (1) year and shall be non-transferable.
  “The Chief of Police shall make his recommendation based upon his investigation of the applicant’s character and conduct as a law abiding person and shall consider past operations, if any, convictions of felonies and crimes involving moral turpitude and connections with criminal elements, taking into consideration the attraction by such establishments of those of tender years.
  “The Chief Building Inspector and City Planner shall determine compliance with applicable building and zoning ordinances of the City.
  “When the City Manager has received the recommendations from the Chief of Police, Chief Building Inspector and City Planner, he shall review such application together with such recommendations as may be furnished and shall approve such application or disapprove same with written notation of his reasons for disapproval.
  “Upon disapproval, the applicant may make such corrections as noted and request approval, request withdrawal and refund of license fee, or give notice of appeal from the City Manager’s decision.
  “In the event of appeal from the City Manager’s decision the applicant shall give written notice of his intention to appeal within ten (10) days of notice of the City Manager’s decision. Such appeal shall be heard by the City Council within thirty (30) days from date of such notice unless a later date is agreed upon by applicant.
  “Upon appeal to the City Council of the City Manager’s decision based upon an adverse recommendation by the Chief of Police as to applicant’s character, the applicant shall have the same burden as prescribed in Article 305, V. A. C. S. to show to the Council that he or it is of good character as a law abiding citizen to such extent that a license should be issued.
  “Upon hearing the Council may reverse the decision of the City Manager in whole or in part or may affirm such decision.
  “An applicant may appeal such decision to the District Court within thirty (30) days but such appeal shall be upon the substantial evidence rule.
  “For violation of any of the requirements of this ordinance the City Manager may upon three (3) days notice of Licensee revoke the license granted hereunder. The same rights of appeal shall exist upon revocation as upon disapproval of the original application.” App. to Juris. Statement 9-10.
  Section 5 provides:
  “It shall be unlawful for any owner, operator or displayer of coin-operated amusement machines to allow any person under the age of seventeen (17) years to play or operate a coin-operated amusement machine unless such minor is accompanied by a parent or legal guardian.” Id., at 8.
  See Ordinance 1310.
  The judgment of the trial court was affirmed by the Texas Court of Civil Appeals, 559 S. W. 2d 92 (1977), and the Texas Supreme Court refused an application for a writ of error, 570 S. W. 2d 377 (1978), finding no reversible error in the conclusion that the denial of the license was not supported by substantial evidence, but declining to reach the vagueness question.
  Section 9 of Ordinance 1353 defined terms used in § 6 of the ordinance (quoted in n. 2, supra), which had been reenacted without change. Section 9 provided in pertinent part:
  “Connection With Criminal Elements is defined as that state of affairs wherein an applicant, or an officer of, principal stockholder of, person having a substantial interest in or management responsibility for, a corporation or other organization wherein such organization is the applicant, directly or as parent, subsidiary or affiliate, has such association, acquaintance, or business association with parties having been convicted of a felony or crime involving moral turpitude or are otherwise involved in unlawful activities, whether convicted or not, to the extent that the fencing of stolen merchandise or illegally obtained funds, the procuring of prostitutes, the transfer or sale of narcotics or illegal substances is made more feasible or likely or the protection of those of tender years from such unwholesome influences are rendered more difficult.
  “A determination by the United States Department of Justice that a party is a member of the ‘mafia’ or ‘Cosa Nostro’ family or that such party is engaged in or affiliated with a nationwide crime organization, whether formally or informally, shall be prima facia evidence, so far as the issuance of a license hereunder, that such person has ‘connections with criminal elements’ and constitute, within the meaning of this ordinance, ‘criminal elements’.” App. to Juris. Statement 12-13.
  434 F. Supp. 473 (1977), aff d in part, rev’d and remanded in part, 630 F. 2d 1029 (1980).
  See Ordinance 1410, App. to Brief for Appellee Al-All.
  If it becomes apparent that a case has become moot while an appeal is pending, the judgment below normally is vacated with directions to dismiss the complaint. See United States v. Munsingwear, Inc., 340 U. S. 36.
  "The test for mootness in cases such as this is a stringent one. Mere voluntary cessation of allegedly illegal conduct does not moot a case; if it did, the courts would be compelled to leave ‘[t]he defendant. . . free to return to his old ways.’ United States v. W. T. Grant Co., 345 U. S. 629, 632 (1953); see, e. g., United States v. Trans-Missouri Freight Assn., 166 U. S. 290 (1897). A case might become moot if subsequent events made it absolutely clear that the allegedly wrongful behavior could not reasonably be expected to recur. ... Of course it is still open to appellees to show, on remand, that the likelihood of further violations is sufficiently remote to make injunctive relief unnecessary. [345 U. S.] at 633-636. This is a matter for the trial judge. But this case is not technically moot, an appeal has been properly taken, and we have no choice but to decide it.” United States v. Concentrated Phosphate Export Assn., 393 U. S. 199, 203-204.
  Indeed, the city has announced just such an intention. See Tr. of Oral Arg. 18-20.
  The Court of Appeals summarized the relevant authorities as follows:
  “A law is void for vagueness if persons ‘of common intelligence must necessarily guess at its meaning and differ as to its application . . . Smith v. Goguen, 415 U. S. 566, 572 n. 8, quoting Connally v. General Construction Co., 269 U. S. 385, 391. See generally Note, The Void-for-Vagueness Doctrine in the Supreme Court, 109 U. Pa. L. Rev. 67 (1960). The offense to due process lies in both the nature and consequences of vagueness. First, vague laws do not give individuals fair notice of the conduct proscribed. Papachristou v. City of Jacksonville, 405 U. S. 156, 162. Accord Grayned v. City of Rockford, 408 U. S. 104, 108 & n. 3. Second, vague laws do not limit the exercise of discretion by law enforcement officials; thus they engender the possiblity of arbitrary and discriminatory enforcement. Grayned v. City of Rockford, 408 U. S. at 108-09 & n. 4; Papachristou v. City of Jacksonville, 405 U. S. at 168-70. Third, vague laws defeat the intrinsic promise of, and frustrate the essence of, a constitutional regime. We remain ‘a government of laws, and not of men,’ Marbury v. Madison, 5 U. S. (1 Cranch.) 137, 163, only so long as our laws remain clear.” 630 F. 2d, at 1037 (citations abbreviated).
  The ordinance is quoted in pertinent part in n. 2, supra.
  Article 1, § 19, of the Texas Constitution provides:
  “No citizen of this State shall be deprived of life, liberty, property, privileges or immunities, or in any manner disfranchised, except by the due course of the law of the land.”
  Article 1, § 3, of the Texas Constitution provides in pertinent part:
  “All free men, when they form a social compact, have equal rights . . . .”
  “Review of a judgment which we cannot disturb, because it rests adequately upon a basis not subject to our examination, would be an anomaly.”
  If this contention is correct, we may review the Court of Appeals’ interpretation of federal law. Cf. Zacchini v. Scripps-Howard Broadcasting Co., 433 U. S. 562, 568; Mental Hygiene Dept. v. Kirchner, 380 U. S. 194, 198; Missouri ex rel. Southern R. Co. v. Mayfield, 340 U. S. 1, 5; Minnesota v. National Tea Co., 309 U. S. 551, 554-555; State Tax Comm’n v. Van Cott, 306 U. S. 511, 514.
  In a section of its opinion entitled “Rational Basis,” the Court of Appeals twice set forth a rational-basis test. See 630 F. 2d, at 1039. In the first paragraph, the court stated that “[t]he test requires that legislative action be rationally related to the accomplishment of a legitimate state purpose,” and cited both federal and state decisions in support of that formulation. In the second paragraph, the court stated that “[t]he test requires that legislation constitute a means that is ‘reasonable, not arbitrary and rests “upon some ground of difference having a fair and substantial relation to the object of the legislation . . . quoting from a decision of the Texas Supreme Court, Texas Woman’s University v. Chayklintaste, 530 S. W. 2d 927, 928 (1975), which in turn quoted from Reed v. Reed, 404 U. S. 71, 76. A number of this Court’s decisions were cited as in accord with this formulation. Although we cannot be sure, we might reasonably infer that the second formulation of the test represents the Court of Appeals’ interpretation of Texas law.
  Our dissenting Brethren suggest that our “view allows federal courts overruling state statutes to avoid appellate review here simply by adding citations to state cases when applying federal law,” post, at 300 (Powell, J., concurring in part and dissenting in part). We are unwilling to assume that any federal judge would discharge his judicial responsibilities in that fashion. In any event, in this case we merely hold that the Court of Appeals must explain the basis for its conclusion, if there be one, that the state ground is adequate and independent of the federal ground.
  Cf. Mental Hygiene Dept. v. Kirchner, supra, at 196-197 (footnotes omitted):
  “The California Supreme Court did not state whether its holding was based on the Equal Protection Clause of the Fourteenth Amendment to the Constitution of the United States or the equivalent provisions of the California Constitution, or both. While we might speculate from the choice of words used in the opinion, and the authorities cited by the court, which provision was the basis for the judgment of the state court, we are unable to say with any degree of certainty that the judgment of the California Supreme Court was not based on an adequate and independent nonfederal ground. This Court is always wary of assuming jurisdiction of a case from a state court unless it -is plain that a federal question is necessarily presented, and the party seeking review here must show that we have jurisdiction of the case. Were we to assume that the federal question was the basis for the decision below, it is clear that the California Supreme Court, either on remand or in another case presenting the same issues, could inform us that its opinion was in fact based, at least in part, on the California Constitution, thus leaving the result untouched by whatever conclusions this Court might have reached on the merits of the federal question. For reasons that follow we conclude that further clarifying proceedings in the California Supreme Court are called for under the principles stated in Minnesota v. National Tea Co., 309 U. S. 551.”
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