MARSHALL, C.J.

Marriage is a vital social institution. The exclusive commitment of two individuals to each other nurtures love and mutual support; it brings stability to our society. For those who choose to marry, and for their children, marriage provides an abundance of legal, financial, and social benefits. In return it imposes weighty legal, financial, and social obligations. The question before us is whether, consistent with the Massachusetts Constitution, the Commonwealth may deny the protections, benefits, and obligations conferred by civil marriage to two individuals of the same sex who wish to marry. We conclude that it may not. The Massachusetts Constitution affirms the dignity and equality of all individuals. It forbids the creation of second-class citizens. In reaching our conclusion we have given full deference to the arguments made by the Commonwealth. But it has failed to identify any constitutionally adequate reason for denying civil marriage to same-sex couples.

We are mindful that our decision marks a change in the history of our marriage law. Many people hold deep-seated religious, moral, and ethical convictions that marriage should be limited to the union of one man and one woman, and that homosexual conduct is immoral. Many hold equally strong religious, moral, and ethical convictions that same-sex couples are entitled to be married, and that homosexual persons should be treated no differently than their heterosexual neighbors. Neither view answers the question before us. Our concern is with the Massachusetts Constitution as a charter of governance for every person properly within its reach. "Our obligation is to define the liberty of all, not to mandate our own moral code." Lawrence v. Texas, 123 S.Ct. 2472, 2480 (2003) (Lawrence ), quoting Planned Parenthood of Southeastern Pa. v. Casey, 505 U.S. 833, 850 (1992).

Whether the Commonwealth may use its formidable regulatory authority to bar same-sex couples from civil marriage is a question not previously addressed by a Massachusetts appellate court. [FN3] It is a question the United States Supreme Court left open as a matter of Federal law in Lawrence, supra at 2484, where it was not an issue. There, the Court affirmed that the core concept of common human dignity protected by the Fourteenth Amendment to the United States Constitution precludes government intrusion into the deeply personal realms of consensual adult expressions of intimacy and one's choice of an intimate partner. The Court also reaffirmed the central role that decisions whether to marry or have children bear in shaping one's identity. Id. at 2481. The Massachusetts Constitution is, if anything, more protective of individual liberty and equality than the Federal Constitution; it may demand broader protection for fundamental rights; and it is less tolerant of government intrusion into the protected spheres of private life.

Barred access to the protections, benefits, and obligations of civil marriage, a person who enters into an intimate, exclusive union with another of the same sex is arbitrarily deprived of membership in one of our community's most rewarding and cherished institutions. That exclusion is incompatible with the constitutional principles of respect for individual autonomy and equality under law.

I
 . . .

In March and April, 2001, each of the plaintiff couples attempted to obtain a marriage license from a city or town clerk's office. As required under G.L. c. 207, they completed notices of intention to marry on forms provided by the registry, see G.L. c. 207, § 20, and presented these forms to a Massachusetts town or city clerk, together with the required health forms and marriage license fees. See G.L. c. 207, § 19. In each case, the clerk either refused to accept the notice of intention to marry or denied a marriage license to the couple on the ground that Massachusetts does not recognize same- sex marriage. [FN4], [FN5] Because obtaining a marriage license is a necessary prerequisite to civil marriage in Massachusetts, denying marriage licenses to the plaintiffs was tantamount to denying them access to civil marriage itself, with its appurtenant social and legal protections, benefits, and obligations. [FN6]
 . . .

II
Although the plaintiffs refer in passing to "the marriage statutes," they focus, quite properly, on G.L. c. 207, the marriage licensing statute, which controls entry into civil marriage. As a preliminary matter, we summarize the provisions of that law.

General Laws c. 207 is both a gatekeeping and a public records statute. It sets minimum qualifications for obtaining a marriage license and directs city and town clerks, the registrar, and the department to keep and maintain certain "vital records" of civil marriages. The gatekeeping provisions of G.L. c. 207 are minimal. They forbid marriage of individuals within certain degrees of consanguinity, §§ 1 and 2, and polygamous marriages. See G.L. c. 207, § 4. See also G.L. c. 207, § 8 (marriages solemnized in violation of §§ 1, 2, and 4, are void ab initio). They prohibit marriage if one of the parties has communicable syphilis, see G.L. c. 207, § 28A, and restrict the circumstances in which a person under eighteen years of age may marry. See G.L. c. 207, §§ 7, 25, and 27. The statute requires that civil marriage be solemnized only by those so authorized. See G.L. c. 207, §§ 38-40.

 . . .
III
A
The larger question is whether, as the department claims, government action that bars same-sex couples from civil marriage constitutes a legitimate exercise of the State's authority to regulate conduct, or whether, as the plaintiffs claim, this categorical marriage exclusion violates the Massachusetts Constitution. We have recognized the long-standing statutory understanding, derived from the common law, that "marriage" means the lawful union of a woman and a man. But that history cannot and does not foreclose the constitutional question.

The plaintiffs' claim that the marriage restriction violates the Massachusetts Constitution can be analyzed in two ways. Does it offend the Constitution's guarantees of equality before the law? Or do the liberty and due process provisions of the Massachusetts Constitution secure the plaintiffs' right to marry their chosen partner? In matters implicating marriage, family life, and the upbringing of children, the two constitutional concepts frequently overlap, as they do here. See, e.g., M.L.B. v. S.L.J., 519 U.S. 102, 120 (1996) (noting convergence of due process and equal protection principles in cases concerning parent-child relationships); Perez v. Sharp, 32 Cal.2d 711, 728 (1948) (analyzing statutory ban on interracial marriage as equal protection violation concerning regulation of fundamental right). See also Lawrence, supra at 2482 ("Equality of treatment and the due process right to demand respect for conduct protected by the substantive guarantee of liberty are linked in important respects, and a decision on the latter point advances both interests"); Bolling v. Sharpe, 347 U.S. 497 (1954) (racial segregation in District of Columbia public schools violates the due process clause of the Fifth Amendment to the United States Constitution), decided the same day as Brown v. Board of Educ. of Topeka, 347 U.S. 483 (1954) (holding that segregation of public schools in the States violates the equal protection clause of the Fourteenth Amendment). Much of what we say concerning one standard applies to the other.

We begin by considering the nature of civil marriage itself. Simply put, the government creates civil marriage. In Massachusetts, civil marriage is, and since pre-Colonial days has been, precisely what its name implies: a wholly secular institution. See Commonwealth v. Munson, 127 Mass. 459, 460-466 (1879) (noting that "[i]n Massachusetts, from very early times, the requisites of a valid marriage have been regulated by statutes of the Colony, Province, and Commonwealth," and surveying marriage statutes from 1639 through 1834). No religious ceremony has ever been required to validate a Massachusetts marriage. Id.

In a real sense, there are three partners to every civil marriage: two willing spouses and an approving State.  . . .

Without question, civil marriage enhances the "welfare of the community." It is a "social institution of the highest importance." French v. McAnarney, supra. Civil marriage anchors an ordered society by encouraging stable relationships over transient ones. It is central to the way the Commonwealth identifies individuals, provides for the orderly distribution of property, ensures that children and adults are cared for and supported whenever possible from private rather than public funds, and tracks important epidemiological and demographic data.

Marriage also bestows enormous private and social advantages on those who choose to marry. Civil marriage is at once a deeply personal commitment to another human being and a highly public celebration of the ideals of mutuality, companionship, intimacy, fidelity, and family. "It is an association that promotes a way of life, not causes; a harmony in living, not political faiths; a bilateral loyalty, not commercial or social projects." Griswold v. Connecticut, 381 U.S. 479, 486 (1965). Because it fulfils yearnings for security, safe haven, and connection that express our common humanity, civil marriage is an esteemed institution, and the decision whether and whom to marry is among life's momentous acts of self-definition.

 . . .

Exclusive marital benefits that are not directly tied to property rights include the presumptions of legitimacy and parentage of children born to a married couple (G.L. c. 209C, § 6, and G.L. c. 46, § 4B); and evidentiary rights, such as the prohibition against spouses testifying against one another about their private conversations, applicable in both civil and criminal cases (G.L. c. 233, § 20). Other statutory benefits of a personal nature available only to married individuals include qualification for bereavement or medical leave to care for individuals related by blood or marriage (G.L. c. 149, § 52D); an automatic "family member" preference to make medical decisions for an incompetent or disabled spouse who does not have a contrary health care proxy, see Shine v. Vega, 429 Mass. 456, 466 (1999); the application of predictable rules of child custody, visitation, support, and removal out-of-State when married parents divorce (e.g., G.L. c. 208, § 19 [temporary custody], § 20 [temporary support], § 28 [custody and support on judgment of divorce], § 30 [removal from Commonwealth], and § 31 [shared custody plan]; priority rights to administer the estate of a deceased spouse who dies without a will, and requirement that surviving spouse must consent to the appointment of any other person as administrator (G.L. c. 38, § 13 [disposition of body], and G.L. c. 113, § 8 [anatomical gifts] ); and the right to interment in the lot or tomb owned by one's deceased spouse (G.L. c. 114, §§ 29-33).

Where a married couple has children, their children are also directly or indirectly, but no less auspiciously, the recipients of the special legal and economic protections obtained by civil marriage. Notwithstanding the Commonwealth's strong public policy to abolish legal distinctions between marital and nonmarital children in providing for the support and care of minors, see Department of Revenue v. Mason M., 439 Mass. 665 (2003); Woodward v. Commissioner of Social Sec., 435 Mass. 536, 546 (2002), the fact remains that marital children reap a measure of family stability and economic security based on their parents' legally privileged status that is largely inaccessible, or not as readily accessible, to nonmarital children. Some of these benefits are social, such as the enhanced approval that still attends the status of being a marital child. Others are material, such as the greater ease of access to family-based State and Federal benefits that attend the presumptions of one's parentage.

It is undoubtedly for these concrete reasons, as well as for its intimately personal significance, that civil marriage has long been termed a "civil right." See, e.g., Loving v. Virginia, 388 U.S. 1, 12 (1967)  . . .
B
For decades, indeed centuries, in much of this country (including Massachusetts) no lawful marriage was possible between white and black Americans. That long history availed not when the Supreme Court of California held in 1948 that a legislative prohibition against interracial marriage violated the due process and equality guarantees of the Fourteenth Amendment, Perez v. Sharp, 32 Cal.2d 711, 728 (1948), or when, nineteen years later, the United States Supreme Court also held that a statutory bar to interracial marriage violated the Fourteenth Amendment, Loving v. Virginia, 388 U.S. 1 (1967). [FN16] As both Perez and Loving make clear, the right to marry means little if it does not include the right to marry the person of one's choice, subject to appropriate government restrictions in the interests of public health, safety, and welfare. See Perez v. Sharp, supra at 717 ("the essence of the right to marry is freedom to join in marriage with the person of one's choice"). See also Loving v. Virginia, supra at 12. In this case, as in Perez and Loving, a statute deprives individuals of access to an institution of fundamental legal, personal, and social significance--the institution of marriage--because of a single trait: skin color in Perez and Loving, sexual orientation here. As it did in Perez and Loving, history must yield to a more fully developed understanding of the invidious quality of the discrimination.

 . . . And central to personal freedom and security is the assurance that the laws will apply equally to persons in similar situations. "Absolute equality before the law is a fundamental principle of our own Constitution." Opinion of the Justices, 211 Mass. 618, 619 (1912). The liberty interest in choosing whether and whom to marry would be hollow if the Commonwealth could, without sufficient justification, foreclose an individual from freely choosing the person with whom to share an exclusive commitment in the unique institution of civil marriage.

The Massachusetts Constitution requires, at a minimum, that the exercise of the State's regulatory authority not be "arbitrary or capricious." Under both the equality and liberty guarantees, regulatory authority must, at very least, serve "a legitimate purpose in a rational way"; a statute must "bear a reasonable relation to a permissible legislative objective." Rushworth v. Registrar of Motor Vehicles, 413 Mass. 265, 270 (1992). See, e.g., Massachusetts Fed'n of Teachers v. Board of Educ., 436 Mass. 763, 778 (2002) (equal protection); Coffee-Rich, Inc. v. Commissioner of Pub. Health, 348 Mass. 414, 422 (1965) (due process). Any law failing to satisfy the basic standards of rationality is void.

The plaintiffs challenge the marriage statute on both equal protection and due process grounds. With respect to each such claim, we must first determine the appropriate standard of review. Where a statute implicates a fundamental right or uses a suspect classification, we employ "strict judicial scrutiny." Lowell v. Kowalski, 380 Mass. 663, 666 (1980). For all other statutes, we employ the " 'rational basis' test." English v. New England Med. Ctr., 405 Mass. 423, 428 (1989). For due process claims, rational basis analysis requires that statutes "bear[ ] a real and substantial relation to the public health, safety, morals, or some other phase of the general welfare." Coffee-Rich, Inc. v. Commissioner of Pub. Health, supra, quoting Sperry & Hutchinson Co. v. Director of the Div. on the Necessaries of Life, 307 Mass. 408, 418 (1940). For equal protection challenges, the rational basis test requires that "an impartial lawmaker could logically believe that the classification would serve a legitimate public purpose that transcends the harm to the members of the disadvantaged class." English v. New England Med. Ctr., supra at 429, quoting Cleburne v. Cleburne Living Ctr., Inc., 473 U.S. 432, 452 (1985) (Stevens, J., concurring).

The department argues that no fundamental right or "suspect" class is at issue here, and rational basis is the appropriate standard of review. For the reasons we explain below, we conclude that the marriage ban does not meet the rational basis test for either due process or equal protection. Because the statute does not survive rational basis review, we do not consider the plaintiffs' arguments that this case merits strict judicial scrutiny.

The department posits three legislative rationales for prohibiting same-sex couples from marrying: (1) providing a "favorable setting for procreation"; (2) ensuring the optimal setting for child rearing, which the department defines as "a two-parent family with one parent of each sex"; and (3) preserving scarce State and private financial resources. We consider each in turn.

The judge in the Superior Court endorsed the first rationale, holding that "the state's interest in regulating marriage is based on the traditional concept that marriage's primary purpose is procreation." This is incorrect. Our laws of civil marriage do not privilege procreative heterosexual intercourse between married people above every other form of adult intimacy and every other means of creating a family. General Laws c. 207 contains no requirement that the applicants for a marriage license attest to their ability or intention to conceive children by coitus. Fertility is not a condition of marriage, nor is it grounds for divorce. People who have never consummated their marriage, and never plan to, may be and stay married. See Franklin v. Franklin, 154 Mass. 515, 516 (1891) ("The consummation of a marriage by coition is not necessary to its validity"). [FN22] People who cannot stir from their deathbed may marry. See G.L. c. 207, § 28A. While it is certainly true that many, perhaps most, married couples have children together (assisted or unassisted), it is the exclusive and permanent commitment of the marriage partners to one another, not the begetting of children, that is the sine qua non of civil marriage.

Moreover, the Commonwealth affirmatively facilitates bringing children into a family regardless of whether the intended parent is married or unmarried, whether the child is adopted or born into a family, whether assistive technology was used to conceive the child, and whether the parent or her partner is heterosexual, homosexual, or bisexual. If procreation were a necessary component of civil marriage, our statutes would draw a tighter circle around the permissible bounds of nonmarital child bearing and the creation of families by noncoital means. The attempt to isolate procreation as "the source of a fundamental right to marry," post at (Cordy, J., dissenting), overlooks the integrated way in which courts have examined the complex and overlapping realms of personal autonomy, marriage, family life, and child rearing. Our jurisprudence recognizes that, in these nuanced and fundamentally private areas of life, such a narrow focus is inappropriate.

The "marriage is procreation" argument singles out the one unbridgeable difference between same-sex and opposite-sex couples, and transforms that difference into the essence of legal marriage. Like "Amendment 2" to the Constitution of Colorado, which effectively denied homosexual persons equality under the law and full access to the political process, the marriage restriction impermissibly "identifies persons by a single trait and then denies them protection across the board." Romer v. Evans, 517 U.S. 620, 633 (1996). In so doing, the State's action confers an official stamp of approval on the destructive stereotype that same-sex relationships are inherently unstable and inferior to opposite-sex relationships and are not worthy of respect.

The department's first stated rationale, equating marriage with unassisted heterosexual procreation, shades imperceptibly into its second: that confining marriage to opposite-sex couples ensures that children are raised in the "optimal" setting. Protecting the welfare of children is a paramount State policy. Restricting marriage to opposite-sex couples, however, cannot plausibly further this policy.  . . . The "best interests of the child" standard does not turn on a parent's sexual orientation or marital status.

The department has offered no evidence that forbidding marriage to people of the same sex will increase the number of couples choosing to enter into opposite-sex marriages in order to have and raise children. There is thus no rational relationship between the marriage statute and the Commonwealth's proffered goal of protecting the "optimal" child rearing unit. Moreover, the department readily concedes that people in same-sex couples may be "excellent" parents. These couples (including four of the plaintiff couples) have children for the reasons others do--to love them, to care for them, to nurture them. But the task of child rearing for same-sex couples is made infinitely harder by their status as outliers to the marriage laws. While establishing the parentage of children as soon as possible is crucial to the safety and welfare of children, see Culliton v. Beth Israel Deaconness Med. Ctr., 435 Mass. 285, 292 (2001), same-sex couples must undergo the sometimes lengthy and intrusive process of second-parent adoption to establish their joint parentage. While the enhanced income provided by marital benefits is an important source of security and stability for married couples and their children, those benefits are denied to families headed by same-sex couples. See, e.g., note 6, supra. While the laws of divorce provide clear and reasonably predictable guidelines for child support, child custody, and property division on dissolution of a marriage, same-sex couples who dissolve their relationships find themselves and their children in the highly unpredictable terrain of equity jurisdiction. See E.N.O. v. L.M.M., supra. Given the wide range of public benefits reserved only for married couples, we do not credit the department's contention that the absence of access to civil marriage amounts to little more than an inconvenience to same-sex couples and their children. Excluding same-sex couples from civil marriage will not make children of opposite-sex marriages more secure, but it does prevent children of same-sex couples from enjoying the immeasurable advantages that flow from the assurance of "a stable family structure in which children will be reared, educated, and socialized." Post at (Cordy, J., dissenting).

No one disputes that the plaintiff couples are families, that many are parents, and that the children they are raising, like all children, need and should have the fullest opportunity to grow up in a secure, protected family unit. Similarly, no one disputes that, under the rubric of marriage, the State provides a cornucopia of substantial benefits to married parents and their children. The preferential treatment of civil marriage reflects the Legislature's conclusion that marriage "is the foremost setting for the education and socialization of children" precisely because it "encourages parents to remain committed to each other and to their children as they grow." Post at (Cordy, J., dissenting).

In this case, we are confronted with an entire, sizeable class of parents raising children who have absolutely no access to civil marriage and its protections because they are forbidden from procuring a marriage license. It cannot be rational under our laws, and indeed it is not permitted, to penalize children by depriving them of State benefits because the State disapproves of their parents' sexual orientation.

 . . .

The department suggests additional rationales for prohibiting same-sex couples from marrying, which are developed by some amici. It argues that broadening civil marriage to include same-sex couples will trivialize or destroy the institution of marriage as it has historically been fashioned. Certainly our decision today marks a significant change in the definition of marriage as it has been inherited from the common law, and understood by many societies for centuries. But it does not disturb the fundamental value of marriage in our society.

Here, the plaintiffs seek only to be married, not to undermine the institution of civil marriage. They do not want marriage abolished. They do not attack the binary nature of marriage, the consanguinity provisions, or any of the other gate-keeping provisions of the marriage licensing law. Recognizing the right of an individual to marry a person of the same sex will not diminish the validity or dignity of opposite-sex marriage, any more than recognizing the right of an individual to marry a person of a different race devalues the marriage of a person who marries someone of her own race. If anything, extending civil marriage to same-sex couples reinforces the importance of marriage to individuals and communities. That same-sex couples are willing to embrace marriage's solemn obligations of exclusivity, mutual support, and commitment to one another is a testament to the enduring place of marriage in our laws and in the human spirit.

It has been argued that, due to the State's strong interest in the institution of marriage as a stabilizing social structure, only the Legislature can control and define its boundaries. Accordingly, our elected representatives legitimately may choose to exclude same-sex couples from civil marriage in order to assure all citizens of the Commonwealth that (1) the benefits of our marriage laws are available explicitly to create and support a family setting that is, in the Legislature's view, optimal for child rearing, and (2) the State does not endorse gay and lesbian parenthood as the equivalent of being raised by one's married biological parents. These arguments miss the point. The Massachusetts Constitution requires that legislation meet certain criteria and not extend beyond certain limits. It is the function of courts to determine whether these criteria are met and whether these limits are exceeded. In most instances, these limits are defined by whether a rational basis exists to conclude that legislation will bring about a rational result. The Legislature in the first instance, and the courts in the last instance, must ascertain whether such a rational basis exists. To label the court's role as usurping that of the Legislature, see, e.g., post at (Cordy, J., dissenting), is to misunderstand the nature and purpose of judicial review. We owe great deference to the Legislature to decide social and policy issues, but it is the traditional and settled role of courts to decide constitutional issues.

The history of constitutional law "is the story of the extension of constitutional rights and protections to people once ignored or excluded." United States v. Virginia, 518 U.S. 515, 557 (1996) (construing equal protection clause of the Fourteenth Amendment to prohibit categorical exclusion of women from public military institute). This statement is as true in the area of civil marriage as in any other area of civil rights. See, e.g., Turner v. Safley, 482 U.S. 78 (1987); Loving v. Virginia, 388 U.S. 1 (1967); Perez v. Sharp, 32 Cal.2d 711 (1948). As a public institution and a right of fundamental importance, civil marriage is an evolving paradigm. The common law was exceptionally harsh toward women who became wives: a woman's legal identity all but evaporated into that of her husband. See generally C.P. Kindregan, Jr., & M.L. Inker, Family Law and Practice §§ 1.9 and 1.10 (3d ed.2002). Thus, one early Nineteenth Century jurist could observe matter of factly that, prior to the abolition of slavery in Massachusetts, "the condition of a slave resembled the connection of a wife with her husband, and of infant children with their father. He is obliged to maintain them, and they cannot be separated from him." Winchendon v. Hatfield, 4 Mass. 123, 129 (1808). But since at least the middle of the Nineteenth Century, both the courts and the Legislature have acted to ameliorate the harshness of the common-law regime. In Bradford v. Worcester, 184 Mass. 557, 562 (1904), we refused to apply the common-law rule that the wife's legal residence was that of her husband to defeat her claim to a municipal "settlement of paupers." In Lewis v. Lewis, 370 Mass. 619, 629 (1976), we abrogated the common-law doctrine immunizing a husband against certain suits because the common-law rule was predicated on "antediluvian assumptions concerning the role and status of women in marriage and in society." Id. at 621. Alarms about the imminent erosion of the "natural" order of marriage were sounded over the demise of antimiscegenation laws, the expansion of the rights of married women, and the introduction of "no-fault" divorce. [FN32] Marriage has survived all of these transformations, and we have no doubt that marriage will continue to be a vibrant and revered institution.

 . ..
The department has had more than ample opportunity to articulate a constitutionally adequate justification for limiting civil marriage to opposite-sex unions. It has failed to do so. The department has offered purported justifications for the civil marriage restriction that are starkly at odds with the comprehensive network of vigorous, gender-neutral laws promoting stable families and the best interests of children. It has failed to identify any relevant characteristic that would justify shutting the door to civil marriage to a person who wishes to marry someone of the same sex.

The marriage ban works a deep and scarring hardship on a very real segment of the community for no rational reason. The absence of any reasonable relationship between, on the one hand, an absolute disqualification of same-sex couples who wish to enter into civil marriage and, on the other, protection of public health, safety, or general welfare, suggests that the marriage restriction is rooted in persistent prejudices against persons who are (or who are believed to be) homosexual. [FN33] "The Constitution cannot control such prejudices but neither can it tolerate them. Private biases may be outside the reach of the law, but the law cannot, directly or indirectly, give them effect." Palmore v. Sidoti, 466 U.S. 429, 433 (1984) (construing Fourteenth Amendment). Limiting the protections, benefits, and obligations of civil marriage to opposite-sex couples violates the basic premises of individual liberty and equality under law protected by the Massachusetts Constitution.

. . .

We construe civil marriage to mean the voluntary union of two persons as spouses, to the exclusion of all others. This reformulation redresses the plaintiffs' constitutional injury and furthers the aim of marriage to promote stable, exclusive relationships. It advances the two legitimate State interests the department has identified: providing a stable setting for child rearing and conserving State resources. It leaves intact the Legislature's broad discretion to regulate marriage. See Commonwealth v. Stowell, 389 Mass. 171, 175 (1983).

In their complaint the plaintiffs request only a declaration that their exclusion and the exclusion of other qualified same-sex couples from access to civil marriage violates Massachusetts law. We declare that barring an individual from the protections, benefits, and obligations of civil marriage solely because that person would marry a person of the same sex violates the Massachusetts Constitution. We vacate the summary judgment for the department. We remand this case to the Superior Court for entry of judgment consistent with this opinion. Entry of judgment shall be stayed for 180 days to permit the Legislature to take such action as it may deem appropriate in light of this opinion. See, e.g., Michaud v. Sheriff of Essex County, 390 Mass. 523, 535-536 (1983).

So ordered.

SOSMAN, J. (dissenting, with whom Spina and Cordy, JJ., join).

In applying the rational basis test to any challenged statutory scheme, the issue is not whether the Legislature's rationale behind that scheme is persuasive to us, but only whether it satisfies a minimal threshold of rationality. Today, rather than apply that test, the court announces that, because it is persuaded that there are no differences between same-sex and opposite-sex couples, the Legislature has no rational basis for treating them differently with respect to the granting of marriage licenses. Reduced to its essence, the court's opinion concludes that, because same-sex couples are now raising children, and withholding the benefits of civil marriage from their union makes it harder for them to raise those children, the State must therefore provide the benefits of civil marriage to same-sex couples just as it does to opposite-sex couples. Of course, many people are raising children outside the confines of traditional marriage, and, by definition, those children are being deprived of the various benefits that would flow if they were being raised in a household with married parents. That does not mean that the Legislature must accord the full benefits of marital status on every household raising children. Rather, the Legislature need only have some rational basis for concluding that, at present, those alternate family structures have not yet been conclusively shown to be the equivalent of the marital family structure that has established itself as a successful one over a period of centuries. People are of course at liberty to raise their children in various family structures, as long as they are not literally harming their children by doing so. See Blixt v. Blixt, 437 Mass. 649, 668-670 (2002) (Sosman, J., dissenting), cert. denied, 537 U.S. 1189 (2003). That does not mean that the State is required to provide identical forms of encouragement, endorsement, and support to all of the infinite variety of household structures that a free society permits.

Based on our own philosophy of child rearing, and on our observations of the children being raised by same-sex couples to whom we are personally close, we may be of the view that what matters to children is not the gender, or sexual orientation, or even the number of the adults who raise them, but rather whether those adults provide the children with a nurturing, stable, safe, consistent, and supportive environment in which to mature. Same-sex couples can provide their children with the requisite nurturing, stable, safe, consistent, and supportive environment in which to mature, just as opposite-sex couples do. It is therefore understandable that the court might view the traditional definition of marriage as an unnecessary anachronism, rooted in historical prejudices that modern society has in large measure rejected and biological limitations that modern science has overcome.

It is not, however, our assessment that matters. Conspicuously absent from the court's opinion today is any acknowledgment that the attempts at scientific study of the ramifications of raising children in same-sex couple households are themselves in their infancy and have so far produced inconclusive and conflicting results. Notwithstanding our belief that gender and sexual orientation of parents should not matter to the success of the child rearing venture, studies to date reveal that there are still some observable differences between children raised by opposite-sex couples and children raised by same-sex couples. See post at--(Cordy, J., dissenting). Interpretation of the data gathered by those studies then becomes clouded by the personal and political beliefs of the investigators, both as to whether the differences identified are positive or negative, and as to the untested explanations of what might account for those differences. (This is hardly the first time in history that the ostensible steel of the scientific method has melted and buckled under the intense heat of political and religious passions.) Even in the absence of bias or political agenda behind the various studies of children raised by same-sex couples, the most neutral and strict application of scientific principles to this field would be constrained by the limited period of observation that has been available. Gay and lesbian couples living together openly, and official recognition of them as their children's sole parents, comprise a very recent phenomenon, and the recency of that phenomenon has not yet permitted any study of how those children fare as adults and at best minimal study of how they fare during their adolescent years. The Legislature can rationally view the state of the scientific evidence as unsettled on the critical question it now faces: Are families headed by same- sex parents equally successful in rearing children from infancy to adulthood as families headed by parents of opposite sexes? Our belief that children raised by same-sex couples should fare the same as children raised in traditional families is just that: a passionately held but utterly untested belief. The Legislature is not required to share that belief but may, as the creator of the institution of civil marriage, wish to see the proof before making a fundamental alteration to that institution.

Although ostensibly applying the rational basis test to the civil marriage statutes, it is abundantly apparent that the court is in fact applying some undefined stricter standard to assess the constitutionality of the marriage statutes' exclusion of same-sex couples. While avoiding any express conclusion as to any of the proffered routes by which that exclusion would be subjected to a test of strict scrutiny--infringement of a fundamental right, discrimination based on gender, or discrimination against gays and lesbians as a suspect classification--the opinion repeatedly alludes to those concepts in a prolonged and eloquent prelude before articulating its view that the exclusion lacks even a rational basis. See, e.g., ante at (noting that State Constitution is "more protective of individual liberty and equality," demands "broader protection for fundamental rights," and is "less tolerant of government intrusion into the protected spheres of private life" than Federal Constitution); ante at (describing decision to marry and choice of marital partner as "among life's momentous acts of self-definition"); ante at-- (repeated references to "right to marry" as "fundamental"); ante at-- (repeated comparisons to statutes prohibiting interracial marriage, which were predicated on suspect classification of race); ante at--(characterizing ban on same-sex marriage as "invidious" discrimination that "deprives individuals of access to an institution of fundamental legal, personal, and social significance" and again noting that Massachusetts Constitution "protects matters of personal liberty against government incursion" more zealously than Federal Constitution); ante at (characterizing "whom to marry, how to express sexual intimacy, and whether and how to establish a family" as "among the most basic of every individual's liberty and due process rights"); ante at ("liberty interest in choosing whether and whom to marry would be hollow" if Commonwealth could "foreclose an individual from freely choosing the person" to marry); ante at (opining that in "overlapping realms of personal autonomy, marriage, family life and child-rearing," characterized as "fundamentally private areas of life," court uses "integrated" analysis instead of "narrow focus"). See also ante at n. 29 (suggesting that prohibition on same-sex marriage "impose[s] limits on personal beliefs"); ante at n. 31] (suggesting that "total deference" to Legislature in this case would be equivalent to "strip[ping]" judiciary "of its constitutional authority to decide challenges" in such areas as forced sterilization, antimiscegenation statutes, and abortion, even though all cited examples pertain to fundamental rights analyzed under strict scrutiny, not under rational basis test); ante at (civil marriage as "a right of fundamental importance"); ante at (noting State policy of "preventing discrimination on the basis of sexual orientation"); ante at, (prohibition against same-sex marriage inconsistent with "gender neutral laws promoting stable families," and "rooted in persistent prejudices against" homosexuals); ante at (prohibition against same-sex marriage "violated the basic premises of individual liberty"). In short, while claiming to apply a mere rational basis test, the court's opinion works up an enormous head of steam by repeated invocations of avenues by which to subject the statute to strict scrutiny, apparently hoping that that head of steam will generate momentum sufficient to propel the opinion across the yawning chasm of the very deferential rational basis test.

Shorn of these emotion-laden invocations, the opinion ultimately opines that the Legislature is acting irrationally when it grants benefits to a proven successful family structure while denying the same benefits to a recent, perhaps promising, but essentially untested alternate family structure. Placed in a more neutral context, the court would never find any irrationality in such an approach. For example, if the issue were government subsidies and tax benefits promoting use of an established technology for energy efficient heating, the court would find no equal protection or due process violation in the Legislature's decision not to grant the same benefits to an inventor or manufacturer of some new, alternative technology who did not yet have sufficient data to prove that that new technology was just as good as the established technology. That the early results from preliminary testing of the new technology might look very promising, or that the theoretical underpinnings of the new technology might appear flawless, would not make it irrational for the Legislature to grant subsidies and tax breaks to the established technology and deny them to the still unproved newcomer in the field. While programs that affect families and children register higher on our emotional scale than programs affecting energy efficiency, our standards for what is or is not "rational" should not be bent by those emotional tugs. Where, as here, there is no ground for applying strict scrutiny, the emotionally compelling nature of the subject matter should not affect the manner in which we apply the rational basis test.

Or, to the extent that the court is going to invoke such emotion-laden and value-laden rhetoric as a means of heightening the degree of scrutiny to be applied, the same form of rhetoric can be employed to justify the Legislature's proceeding with extreme caution in this area. In considering whether the Legislature has a rational reason for postponing a dramatic change to the definition of marriage, it is surely pertinent to the inquiry to recognize that this proffered change affects not just a load-bearing wall of our social structure but the very cornerstone of that structure. See post at--(Cordy, J., dissenting). Before making a fundamental alteration to that cornerstone, it is eminently rational for the Legislature to require a high degree of certainty as to the precise consequences of that alteration, to make sure that it can be done safely, without either temporary or lasting damage to the structural integrity of the entire edifice. The court today blithely assumes that there are no such dangers and that it is safe to proceed (see ante at--, an assumption that is not supported by anything more than the court's blind faith that it is so.

More importantly, it is not our confidence in the lack of adverse consequences that is at issue, or even whether that confidence is justifiable. The issue is whether it is rational to reserve judgment on whether this change can be made at this time without damaging the institution of marriage or adversely affecting the critical role it has played in our society. Absent consensus on the issue (which obviously does not exist), or unanimity amongst scientists studying the issue (which also does not exist), or a more prolonged period of observation of this new family structure (which has not yet been possible), it is rational for the Legislature to postpone any redefinition of marriage that would include same-sex couples until such time as it is certain that that redefinition will not have unintended and undesirable social consequences. Through the political process, the people may decide when the benefits of extending civil marriage to same-sex couples have been shown to outweigh whatever risks--be they palpable or ephemeral--are involved. However minimal the risks of that redefinition of marriage may seem to us from our vantage point, it is not up to us to decide what risks society must run, and it is inappropriate for us to abrogate that power to ourselves merely because we are confident that "it is the right thing to do." Ante at (Greaney, J., concurring).

As a matter of social history, today's opinion may represent a great turning point that many will hail as a tremendous step toward a more just society. As a matter of constitutional jurisprudence, however, the case stands as an aberration. To reach the result it does, the court has tortured the rational basis test beyond recognition. I fully appreciate the strength of the temptation to find this particular law unconstitutional--there is much to be said for the argument that excluding gay and lesbian couples from the benefits of civil marriage is cruelly unfair and hopelessly outdated; the inability to marry has a profound impact on the personal lives of committed gay and lesbian couples (and their children) to whom we are personally close (our friends, neighbors, family members, classmates, and co-workers); and our resolution of this issue takes place under the intense glare of national and international publicity. Speaking metaphorically, these factors have combined to turn the case before us into a "perfect storm" of a constitutional question. In my view, however, such factors make it all the more imperative that we adhere precisely and scrupulously to the established guideposts of our constitutional jurisprudence, a jurisprudence that makes the rational basis test an extremely deferential one that focuses on the rationality, not the persuasiveness, of the potential justifications for the classifications in the legislative scheme. I trust that, once this particular "storm" clears, we will return to the rational basis test as it has always been understood and applied. Applying that deferential test in the manner it is customarily applied, the exclusion of gay and lesbian couples from the institution of civil marriage passes constitutional muster. I respectfully dissent.

CORDY, J. (dissenting, with whom Spina and Sosman, JJ., join).

The court's opinion concludes that the Department of Public Health has failed to identify any "constitutionally adequate reason" for limiting civil marriage to opposite-sex unions, and that there is no "reasonable relationship" between a disqualification of same-sex couples who wish to enter into a civil marriage and the protection of public health, safety, or general welfare. Consequently, it holds that the marriage statute cannot withstand scrutiny under the Massachusetts Constitution. Because I find these conclusions to be unsupportable in light of the nature of the rights and regulations at issue, the presumption of constitutional validity and significant deference afforded to legislative enactments, and the "undesirability of the judiciary substituting its notions of correct policy for that of a popularly elected Legislature" responsible for making such policy, Zayre Corp. v. Attorney Gen., 372 Mass. 423, 433 (1977), I respectfully dissent. Although it may be desirable for many reasons to extend to same-sex couples the benefits and burdens of civil marriage (and the plaintiffs have made a powerfully reasoned case for that extension), that decision must be made by the Legislature, not the court.

 . . .

The Massachusetts marriage statute does not impair the exercise of a recognized fundamental right, or discriminate on the basis of sex in violation of the equal rights amendment to the Massachusetts Constitution. Consequently, it is subject to review only to determine whether it satisfies the rational basis test. Because a conceivable rational basis exists upon which the Legislature could conclude that the marriage statute furthers the legitimate State purpose of ensuring, promoting, and supporting an optimal social structure for the bearing and raising of children, it is a valid exercise of the State's police power.

A. Limiting marriage to the union of one man and one woman does not impair the exercise of a fundamental right. Civil marriage is an institution created by the State. In Massachusetts, the marriage statutes are derived from English common law, see Commonwealth v. Knowlton, 2 Mass. 530, 534 (1807), and were first enacted in colonial times. Commonwealth v. Munson, 127 Mass. 459, 460 (1879). They were enacted to secure public interests and not for religious purposes or to promote personal interests or aspirations. (See discussion infra at--). As the court notes in its opinion, the institution of marriage is "the legal union of a man and woman as husband and wife," ante at, and it has always been so under Massachusetts law, colonial or otherwise.

The plaintiffs contend that because the right to choose to marry is a "fundamental" right, the right to marry the person of one's choice, including a member of the same sex, must also be a "fundamental" right. While the court stops short of deciding that the right to marry someone of the same sex is "fundamental" such that strict scrutiny must be applied to any statute that impairs it, it nevertheless agrees with the plaintiffs that the right to choose to marry is of fundamental importance ("among the most basic" of every person's "liberty and due process rights") and would be "hollow" if an individual was foreclosed from "freely choosing the person with whom to share ... the ... institution of civil marriage." Ante at. Hence, it concludes that a marriage license cannot be denied to an individual who wishes to marry someone of the same sex. In reaching this result the court has transmuted the "right" to marry into a right to change the institution of marriage itself. This feat of reasoning succeeds only if one accepts the proposition that the definition of the institution of marriage as a union between a man and a woman is merely "conclusory" (as suggested, ante at [Greaney, J., concurring] ), rather than the basis on which the "right" to partake in it has been deemed to be of fundamental importance. In other words, only by assuming that "marriage" includes the union of two persons of the same sex does the court conclude that restricting marriage to opposite-sex couples infringes on the "right" of same-sex couples of "marry." [FN2]

The plaintiffs ground their contention that they have a fundamental right to marry a person of the same sex in a long line of Supreme Court decisions, e.g., Turner v. Safley, 482 U.S. 78 (1987); Zablocki v. Redhail, 434 U.S. 374 (1978); Loving v. Virginia, 388 U.S. 1 (1967); Griswold v. Connecticut, 381 U.S. 479 (1965); Skinner v. Oklahoma, 316 U.S. 535 (1942); that discuss the importance of marriage. In context, all of these decisions and their discussions are about the "fundamental" nature of the institution of marriage as it has existed and been understood in this country, not as the court has redefined it today. Even in that context, its "fundamental" nature is derivative of the nature of the interests that underlie or are associated with it. An examination of those interests reveals that they are either not shared by same-sex couples or not implicated by the marriage statutes.

Supreme Court cases that have described marriage or the right to marry as "fundamental" have focused primarily on the underlying interest of every individual in procreation, which, historically, could only legally occur within the construct of marriage because sexual intercourse outside of marriage was a criminal act. In Skinner v. Oklahoma, supra, the first case to characterize marriage as a "fundamental" right, the Supreme Court stated, as its rationale for striking down a sterilization statute, that "[m]arriage and procreation are fundamental to the very existence of the race." Id. at 541. In concluding that a sterilized individual "is forever deprived of a basic liberty," id., the Court was obviously referring to procreation rather than marriage, as this court recognized in Matter of Moe, 385 Mass. 555, 560 (1982). Similarly, in Loving v. Virginia, supra, in which the United States Supreme Court struck down Virginia's antimiscegenation statute, the Court implicitly linked marriage with procreation in describing marriage as "fundamental to our very existence." Id. at 12. In Zablocki v. Redhail, supra, the Court expressly linked the right to marry with the right to procreate, concluding that "if [the plaintiff's] right to procreate means anything at all, it must imply some right to enter the only relationship in which the State ... allows sexual relations legally to take place." Id. at 386. Once again, in Turner v. Safley, supra, striking a State regulation that curtailed the right of an inmate to marry, the Court included among the important attributes of such marriages the "expectation that [the marriage] ultimately will be fully consummated." Id. at 96. See Milford v. Worcester, 7 Mass. 48, 52 (1810) (purpose of marriage is "to regulate, chasten, and refine, the intercourse between the sexes; and to multiply [and] preserve ... the species"). Because same-sex couples are unable to procreate on their own, any right to marriage they may possess cannot be based on their interest in procreation, which has been essential to the Supreme Court's denomination of the right to marry as fundamental.

Supreme Court cases recognizing a right to privacy in intimate decision-making, e.g., Griswold v. Connecticut, supra (striking down statute prohibiting use of contraceptives); Roe v. Wade, 410 U.S. 113 (1973) (striking down statute criminalizing abortion), have also focused primarily on sexual relations and the decision whether or not to procreate, and have refused to recognize an "unlimited right" to privacy. Id. at 154. Massachusetts courts have been no more willing than the Federal courts to adopt a "universal[ ]" "privacy doctrine," Marcoux v. Attorney Gen., 375 Mass. 63, 67 (1978), or to derive "controversial 'new' rights from the Constitution." Aime v. Commonwealth, 414 Mass. 667, 674 n. 10 (1993).

What the Griswold Court found "repulsive to the notions of privacy surrounding the marriage relationship" was the prospect of "allow[ing] the police to search the sacred precincts of marital bedrooms for telltale signs of the use of contraceptives." Griswold v. Connecticut, supra at 485-486. See Moe v. Secretary of Admin. & Fin., 382 Mass. 629, 658 (1981), quoting L. Tribe, American Constitutional Law 924 (1978) (finding it "difficult to imagine a clearer case of bodily intrusion" than being forced to bear a child). When Justice Goldberg spoke of "marital relations" in the context of finding it "difficult to imagine what is more private or more intimate than a husband and wife's marital relations[hip]," Griswold v. Connecticut, supra at 495 (Goldberg, J., concurring), he was obviously referring to sexual relations. [FN5] Similarly, in Lawrence v. Texas, 123 S.Ct. 2472 (2003), it was the criminalization of private sexual behavior that the Court found violative of the petitioners' liberty interest.

In Massachusetts jurisprudence, protected decisions generally have been limited to those concerning "whether or not to beget or bear a child," Matter of Moe, 385 Mass. 555, 564 (1982) (see Opinion of the Justices, 423 Mass. 1201, 1234-1235 [1996] ["focus of (the Griswold and Roe cases) and the cases following them has been the intrusion ... into the especially intimate aspects of a person's life implicated in procreation and childbearing"] ); how to raise a child, see Care & Protection of Robert, 408 Mass. 52, 58, 60 (1990); or whether or not to accept medical treatment, see Brophy v. New England Sinai Hosp., Inc., 398 Mass. 417, 430 (1986); Superintendent of Belchertown State Sch. v. Saikewicz, 373 Mass. 728, 742 (1977), none of which is at issue here. See also Commonwealth v. Balthazar, 366 Mass. 298, 301 (1974) (statute punishing unnatural and lascivious acts does not apply to sexual conduct engaged in by adults in private, in light of "articulation of the constitutional right of an individual to be free from government regulation of certain sex related activities").

 . . .

While the institution of marriage is deeply rooted in the history and traditions of our country and our State, the right to marry someone of the same sex is not. No matter how personal or intimate a decision to marry someone of the same sex might be, the right to make it is not guaranteed by the right of personal autonomy.

 . ..

Finally, the constitutionally protected interest in child rearing, recognized in Meyer v. Nebraska, 262 U.S. 390, 399 (1923); Pierce v. Society of Sisters, 268 U.S. 510, 534-535 (1925); and Care & Protection of Robert, supra at 58, 60, is not implicated or infringed by the marriage statute here. The fact that the plaintiffs cannot marry has no bearing on their independently protected constitutional rights as parents which, as with opposite-sex parents, are limited only by their continued fitness and the best interests of their children. Bezio v. Patenaude, 381 Mass. 563, 579 (1980) (courts may not use parent's sexual orientation as reason to deny child custody).

Because the rights and interests discussed above do not afford the plaintiffs any fundamental right that would be impaired by a statute limiting marriage to members of the opposite sex, they have no fundamental right to be declared "married" by the State.

Insofar as the right to marry someone of the same sex is neither found in the unique historical context of our Constitution nor compelled by the meaning ascribed by this court to the liberty and due process protections contained within it, should the court nevertheless recognize it as a fundamental right? The consequences of deeming a right to be "fundamental" are profound, and this court, as well as the Supreme Court, has been very cautious in recognizing them. Such caution is required by separation of powers principles. If a right is found to be "fundamental," it is, to a great extent, removed from "the arena of public debate and legislative action"; utmost care must be taken when breaking new ground in this field "lest the liberty protected by the Due Process Clause be subtly transformed into the policy preferences of [judges]." Washington v. Glucksberg, 521 U.S. 702, 720 (1997).

 . . .

This is not to say that a statute that has no rational basis must nevertheless be upheld as long as it is of ancient origin. However, "[t]he long history of a certain practice ... and its acceptance as an uncontroversial part of our national and State tradition do suggest that [the court] should reflect carefully before striking it down." Colo v. Treasurer & Receiver Gen., 378 Mass. 550, 557 (1979). As this court has recognized, the "fact that a challenged practice 'is followed by a large number of states ... is plainly worth considering in determining whether the practice "offends some principle of justice so rooted in the traditions and conscience of our people as to be ranked as fundamental." ' " Commonwealth v. Kostka, 370 Mass. 516, 533 (1976), quoting Leland v. Oregon, 343 U.S. 790, 798 (1952).

 . . . In such circumstances, the law with respect to same- sex marriages must be left to develop through legislative processes, subject to the constraints of rationality, lest the court be viewed as using the liberty and due process clauses as vehicles merely to enforce its own views regarding better social policies, a role that the strongly worded separation of powers principles in art. 30 of the Declaration of Rights of our Constitution forbids, and for which the court is particularly ill suited.

 . . .
C. The marriage statute satisfies the rational basis standard. The burden of demonstrating that a statute does not satisfy the rational basis standard rests on the plaintiffs. It is a weighty one. "[A] reviewing court will presume a statute's validity, and make all rational inferences in favor of it.... The Legislature is not required to justify its classifications, nor provide a record or finding in support of them." (Citation omitted.)  . . .
In analyzing whether a statute satisfies the rational basis standard, we look to the nature of the classification embodied in the enactment, then to whether the statute serves a legitimate State purpose, and finally to whether the classification is reasonably related to the furtherance of that purpose. . . .

Civil marriage is the institutional mechanism by which societies have sanctioned and recognized particular family structures, and the institution of marriage has existed as one of the fundamental organizing principles of human society.  . . .
Paramount among its many important functions, the institution of marriage has systematically provided for the regulation of heterosexual behavior, brought order to the resulting procreation, and ensured a stable family structure in which children will be reared, educated, and socialized . . .  Admittedly, heterosexual intercourse, procreation, and child care are not necessarily conjoined (particularly in the modern age of widespread effective contraception and supportive social welfare programs), but an orderly society requires some mechanism for coping with the fact that sexual intercourse commonly results in pregnancy and childbirth. The institution of marriage is that mechanism.

The institution of marriage provides the important legal and normative link between heterosexual intercourse and procreation on the one hand and family responsibilities on the other. The partners in a marriage are expected to engage in exclusive sexual relations, with children the probable result and paternity presumed. See G.L. c. 209C, § 6 ("a man is presumed to be the father of a child ... if he is or has been married to the mother and the child was born during the marriage, or within three hundred days after the marriage was terminated by death, annulment or divorce"). Whereas the relationship between mother and child is demonstratively and predictably created and recognizable through the biological process of pregnancy and childbirth, there is no corresponding process for creating a relationship between father and child. Similarly, aside from an act of heterosexual intercourse nine months prior to childbirth, there is no process for creating a relationship between a man and a woman as the parents of a particular child. The institution of marriage fills this void by formally binding the husband-father to his wife and child, and imposing on him the responsibilities of fatherhood. See J.Q. Wilson, supra at 23-32. See also P. Blumstein & P. Schwartz, supra at 29; C.N. Degler, supra at 61; G. Douglas, supra at 223; S.L. Nock, supra at 7; L. Saxton, supra at 239-240, 242; M.A. Schwartz & B.M. Scott, supra at 4-6; Wardle, supra at 781-796. The alternative, a society without the institution of marriage, in which heterosexual intercourse, procreation, and child care are largely disconnected processes, would be chaotic.

The marital family is also the foremost setting for the education and socialization of children. Children learn about the world and their place in it primarily from those who raise them, and those children eventually grow up to exert some influence, great or small, positive or negative, on society. The institution of marriage encourages parents to remain committed to each other and to their children as they grow, thereby encouraging a stable venue for the education and socialization of children. See P. Blumstein & P. Schwartz, supra at 26; C.N. Degler, supra at 61; S.L. Nock, supra at 2-3; C. Lasch, supra at 81; M.A. Schwartz & B.M. Scott, supra at 6-7. More macroscopically, construction of a family through marriage also formalizes the bonds between people in an ordered and institutional manner, thereby facilitating a foundation of interconnectedness and interdependency on which more intricate stabilizing social structures might be built. See M. Grossberg, Governing the Hearth: Law and Family in Nineteenth-Century America 10 (1985); C. Lasch, supra; L. Saxton, supra at 260; J.Q. Wilson, supra at 221.

This court, among others, has consistently acknowledged both the institutional importance of marriage as an organizing principle of society, and the State's interest in regulating it. See French v. McAnarney, 290 Mass. 544, 546 (1935) ("Marriage is not merely a contract between the parties. It is the foundation of the family. It is a social institution of the highest importance. The Commonwealth has a deep interest that its integrity is not jeopardized"); Milford v. Worcester, 7 Mass. 48, 52 (1810) ("Marriage, being essential to the peace and harmony, and to the virtues and improvements of civil society, it has been, in all well-regulated governments, among the first attentions of the civil magistrate to regulate [it]"). See also Skinner v. Oklahoma, 316 U.S. 535, 541 (1942) ("Marriage and procreation are fundamental to the very existence and survival of the [human] race"); Maynard v. Hill, 125 U.S. 190, 211 (1888) (marriage "is an institution, in the maintenance of which in its purity the public is deeply interested, for it is the foundation of the family and of society, without which there would be neither civilization nor progress"); Murphy v. Ramsey, 114 U.S. 15, 45 (1885) ("no legislation can be supposed more wholesome and necessary in the founding of a free, self-governing commonwealth ... than that which seeks to establish it on the basis of the idea of the family, as consisting in and springing from the union for life of one man and one woman ... the sure foundation of all that is stable and noble in our civilization; the best guaranty of that reverent morality which is the source of all beneficent progress in social and political improvement"); Reynolds v. United States, 98 U.S. 145, 165 (1878) ("Upon [marriage] society may be said to be built, and out of its fruits spring social relations and social obligations and duties, with which government is necessarily required to deal").

It is undeniably true that dramatic historical shifts in our cultural, political, and economic landscape have altered some of our traditional notions about marriage, including the interpersonal dynamics within it, the range of responsibilities required of it as an institution, and the legal environment in which it exists. Nevertheless, the institution of marriage remains the principal weave of our social fabric.  . . . A family defined by heterosexual marriage continues to be the most prevalent social structure into which the vast majority of children are born, nurtured, and prepared for productive participation in civil society, see Children's Living Arrangements and Characteristics: March, 2002, United States Census Bureau Current Population Reports at 3 (June, 2003) (in 2002, 69% of children lived with two married parents, 23% lived with their mother, 5% lived with their father, and 4% lived in households with neither parent present).

It is difficult to imagine a State purpose more important and legitimate than ensuring, promoting, and supporting an optimal social structure within which to bear and raise children. At the very least, the marriage statute continues to serve this important State purpose.

3. Rational relationship. The question we must turn to next is whether the statute, construed as limiting marriage to couples of the opposite sex, remains a rational way to further that purpose. Stated differently, we ask whether a conceivable rational basis exists on which the Legislature could conclude that continuing to limit the institution of civil marriage to members of the opposite sex furthers the legitimate purpose of ensuring, promoting, and supporting an optimal social structure for the bearing and raising of children.

In considering whether such a rational basis exists, we defer to the decision- making process of the Legislature, and must make deferential assumptions about the information that it might consider and on which it may rely . . . We must assume that the Legislature (1) might conclude that the institution of civil marriage has successfully and continually provided this structure over several centuries; (2) might consider and credit studies that document negative consequences that too often follow children either born outside of marriage or raised in households lacking either a father or a mother figure, and scholarly commentary contending that children and families develop best when mothers and fathers are partners in their parenting; and (3) would be familiar with many recent studies that variously: support the proposition that children raised in intact families headed by same-sex couples fare as well on many measures as children raised in similar families headed by opposite-sex couples; support the proposition that children of same-sex couples fare worse on some measures; or reveal notable differences between the two groups of children that warrant further study.

We must also assume that the Legislature would be aware of the critiques of the methodologies used in virtually all of the comparative studies of children raised in these different environments, cautioning that the sampling populations are not representative, that the observation periods are too limited in time, that the empirical data are unreliable, and that the hypotheses are too infused with political or agenda driven bias . . .
Taking all of this available information into account, the Legislature could rationally conclude that a family environment with married opposite-sex parents remains the optimal social structure in which to bear children, and that the raising of children by same-sex couples, who by definition cannot be the two sole biological parents of a child and cannot provide children with a parental authority figure of each gender, presents an alternative structure for child rearing that has not yet proved itself beyond reasonable scientific dispute to be as optimal as the biologically based marriage norm . . . Working from the assumption that a recognition of same-sex marriages will increase the number of children experiencing this alternative, the Legislature could conceivably conclude that declining to recognize same-sex marriages remains prudent until empirical questions about its impact on the upbringing of children are resolved.

The fact that the Commonwealth currently allows same-sex couples to adopt, see Adoption of Tammy, 416 Mass. 205 (1993), does not affect the rationality of this conclusion. The eligibility of a child for adoption presupposes that at least one of the child's biological parents is unable or unwilling, for some reason, to participate in raising the child. In that sense, society has "lost" the optimal setting in which to raise that child--it is simply not available. In these circumstances, the principal and overriding consideration is the "best interests of the child," considering his or her unique circumstances and the options that are available for that child. The objective is an individualized determination of the best environment for a particular child, where the normative social structure--a home with both the child's biological father and mother--is not an option. That such a focused determination may lead to the approval of a same-sex couple's adoption of a child does not mean that it would be irrational for a legislator, in fashioning statutory laws that cannot make such individualized determinations, to conclude generally that being raised by a same-sex couple has not yet been shown to be the absolute equivalent of being raised by one's married biological parents.

That the State does not preclude different types of families from raising children does not mean that it must view them all as equally optimal and equally deserving of State endorsement and support. For example, single persons are allowed to adopt children, but the fact that the Legislature permits single-parent adoption does not mean that it has endorsed single parenthood as an optimal setting in which to raise children or views it as the equivalent of being raised by both of one's biological parents.  The same holds true with respect to same-sex couples--the fact that they may adopt children means only that the Legislature has concluded that they may provide an acceptable setting in which to raise children who cannot be raised by both of their biological parents. The Legislature may rationally permit adoption by same-sex couples yet harbor reservations as to whether parenthood by same-sex couples should be affirmatively encouraged to the same extent as parenthood by the heterosexual couple whose union produced the child.

In addition, the Legislature could conclude that redefining the institution of marriage to permit same-sex couples to marry would impair the State's interest in promoting and supporting heterosexual marriage as the social institution that it has determined best normalizes, stabilizes, and links the acts of procreation and child rearing. While the plaintiffs argue that they only want to take part in the same stabilizing institution, the Legislature conceivably could conclude that permitting their participation would have the unintended effect of undermining to some degree marriage's ability to serve its social purpose. See Commonwealth v. Stowell, 389 Mass. 171, 175 (1983) (given State's broad concern with institution of marriage, it has "legitimate interest in prohibiting conduct which may threaten that institution").

As long as marriage is limited to opposite-sex couples who can at least theoretically procreate, society is able to communicate a consistent message to its citizens that marriage is a (normatively) necessary part of their procreative endeavor; that if they are to procreate, then society has endorsed the institution of marriage as the environment for it and for the subsequent rearing of their children; and that benefits are available explicitly to create a supportive and conducive atmosphere for those purposes. If society proceeds similarly to recognize marriages between same-sex couples who cannot procreate, it could be perceived as an abandonment of this claim, and might result in the mistaken view that civil marriage has little to do with procreation: just as the potential of procreation would not be necessary for a marriage to be valid, marriage would not be necessary for optimal procreation and child rearing to occur. In essence, the Legislature could conclude that the consequence of such a policy shift would be a diminution in society's ability to steer the acts of procreation and child rearing into their most optimal setting. [FN36] Hall-Omar Baking Co. v. Commissioner of Labor & Indus., 344 Mass. 695, 700 (1962) ("Legislative classification is valid if it is rational and bears some relationship to the object intended to be accomplished" [emphasis added] ).

The court recognizes this concern, but brushes it aside with the assumption that permitting same-sex couples to marry "will not diminish the validity or dignity of opposite-sex marriage," ante at, and that "we have no doubt that marriage will continue to be a vibrant and revered institution." Ante at. Whether the court is correct in its assumption is irrelevant. What is relevant is that such predicting is not the business of the courts. A rational Legislature, given the evidence, could conceivably come to a different conclusion, or could at least harbor rational concerns about possible unintended consequences of a dramatic redefinition of marriage.

There is no question that many same-sex couples are capable of being good parents, and should be (and are) permitted to be so. The policy question that a legislator must resolve is a different one, and turns on an assessment of whether the marriage structure proposed by the plaintiffs will, over time, if endorsed and supported by the State, prove to be as stable and successful a model as the one that has formed a cornerstone of our society since colonial times, or prove to be less than optimal, and result in consequences, perhaps now unforeseen, adverse to the State's legitimate interest in promoting and supporting the best possible social structure in which children should be born and raised. Given the critical importance of civil marriage as an organizing and stabilizing institution of society, it is eminently rational for the Legislature to postpone making fundamental changes to it until such time as there is unanimous scientific evidence, or popular consensus, or both, that such changes can safely be made.

 . . .
D. Conclusion. While "the Massachusetts Constitution protects matters of personal liberty against government intrusion at least as zealously, and often more so than does the Federal Constitution," ante at--, this case is not about government intrusions into matters of personal liberty. It is not about the rights of same-sex couples to choose to live together, or to be intimate with each other, or to adopt and raise children together. It is about whether the State must endorse and support their choices by changing the institution of civil marriage to make its benefits, obligations, and responsibilities applicable to them. While the courageous efforts of many have resulted in increased dignity, rights, and respect for gay and lesbian members of our community, the issue presented here is a profound one, deeply rooted in social policy, that must, for now, be the subject of legislative not judicial action.