When California voters exercise their power of initiative, a simple majority vote is sufficient to amend any part of the state Constitution. (Cal. Const., art. XVIII, §§ 3, 4.) To determine whether the voters have validly exercised this power, a judge must put aside any personal views and apply the law as set forth in the state Constitution and in this court’s previous decisions. And when the voters have validly exercised this power, as they did here, a judge must enforce the Constitution as amended.
One year ago, this court decided that California’s statutory law denying same-sex couples the right to marry violated the privacy, due process, and equal protection provisions of our state Constitution as it then read. (In re Marriage Cases (2008) 43 Cal.4th 757 [76 Cal.Rptr.3d 683, 183 P.3d 384] (Marriage Cases).) I signed the majority opinion in that case, and I also authored a concurring opinion in which I answered the argument that the marriage rights of same-sex couples did not present an issue of constitutional law for this court to decide but instead was essentially a social or political controversy inappropriate for judicial resolution. In my separate opinion, I wrote: “Absent a compelling justification, our state government may not deny a right as fundamental as marriage to any segment of society. Whether an unconstitutional denial of a fundamental right has occurred is not a matter to be decided by the executive or legislative branch, or by popular vote, but is instead an issue of constitutional law for resolution by the judicial branch of state government. Indeed, this court’s decision in Lockyer [v. City and County of San Francisco (2004) 33 Cal.4th 1055 [17 Cal.Rptr.3d 225, 95 P.3d 459]] made it clear that the courts alone must decide whether excluding individuals from marriage because of sexual orientation can be reconciled with our state Constitution’s equal protection guarantee. (Lockyer, supra, 33 Cal.4th at pp. 1068-1069.) The court today discharges its constitutional obligation by resolving that issue.” (Marriage Cases, supra, 43 Cal.4th at p. 860 (conc. opn. of Kennard, J.).) My view on this issue has not changed: Interpreting and enforcing the state Constitution is a judicial responsibility, and the judiciary’s duty to exercise this authority is particularly important and grave when constitutionally guaranteed rights and freedoms are at stake. What has changed, however, is the state Constitution that this court interpreted and enforced in the Marriage Cases.
*476Shortly after this court’s decision in the Marriage Cases, supra, 43 Cal.4th 757, California’s voters by initiative changed the text of our state Constitution by adding a new section 7.5 to article I. It reads: “Only marriage between a man and a woman is valid or recognized in California.” The main issue before the court here is the validity of that alteration in the language of our state’s fundamental charter, which expressly recognizes the people’s right to enact constitutional amendments by initiative (Cal. Const., art. II, § 8, subd. (a)).
Although the people through the initiative power may not change this court’s interpretation of language in the state Constitution, they may change the constitutional language itself, and thereby enlarge or reduce the personal rights that the state Constitution as so amended will thereafter guarantee and protect. The difference between interpretation and alteration is the difference between the judicial and legislative powers. Interpretation of existing statutory and constitutional provisions is a fundamental power of the judicial branch, while alteration of existing statutory and constitutional provisions—by addition, deletion, or modification—is a fundamental legislative power that the people may exercise through the initiative process. Although this court’s decision in the Marriage Cases, supra, 43 Cal.4th 757, remains the final word on the meaning of the state Constitution as it then read, the people have now used their initiative power to refashion the wording of the California Constitution and by this means have altered its substance, and thus its meaning, as of the effective date of the initiative measure.
For the reasons explained in the majority opinion, petitioners have failed to establish any legal basis to invalidate the initiative measure that added section 7.5 to article I of our state Constitution. Because it did not fundamentally alter California’s state governmental plan, this initiative measure could validly be enacted by the procedures prescribed for constitutional amendments rather than the more rigorous procedures prescribed for constitutional revisions. (See Cal. Const., art. XVIII, §§ 1-4.) Because it does not restrict or impair this court’s authority to interpret and enforce the state Constitution, the initiative measure does not violate the separation of powers doctrine. And, contrary to the Attorney General’s contention, the state Constitution does not prohibit constitutional amendments qualifying or restricting rights that the state Constitution describes as “inalienable,” nor does it require that such amendments be supported by a compelling interest.
Unlike the state Constitution that this court interpreted in the Marriage Cases, supra, 43 Cal.4th 757, the currently existing California Constitution, while continuing to protect the rights of same-sex couples to form officially recognized family relationships, now restricts marriage to opposite-sex couples. As members of the judicial branch, the justices of this court have a *477solemn obligation to interpret and enforce the entire state Constitution, including that new and valid voter-enacted restriction. Indeed, in deciding that section 7.5 of article I of the state Constitution does not invalidate the marriages of same-sex couples performed before its effective date (see maj. opn., ante, at p. 474), this court has already begun to discharge its constitutional obligation to interpret and apply that provision.
With these observations, I concur fully in the court’s opinion authored by the Chief Justice.