The majority decision framed the question to be answered as follows:

Whether our state Constitution prohibits the state from establishing a statutory scheme in which both opposite-sex and same-sex couples are granted the right to enter into an officially recognized family relationship that affords all of the significant legal rights and obligations traditionally associated under state law with the institution of marriage, but under which the union of an opposite-sex couple is officially designated a "marriage" whereas the union of a same-sex couple is officially designated a "domestic partnership." The question we must address is whether, under these circumstances, the failure to designate the official relationship of same-sex couples as marriage violates the California Constitution.

In plainer English, is it acceptable under the California constitution for the state to have two separate-but-mostly-equal institutions: marriage for straights and domestic partnerships for gays?

The answer: no. These parallel institutions violate both the fundamental right to marry and the guarantee of equal protection. I'll tackle each of these in turn.

The right to marry

Case law makes it very clear that the California constitution embodies a right to marry that is fundamental. In the words of the court, "the right to marry represents the right of an individual to establish a legally recognized family with the person of one's choice, and, as such, is of fundamental significance both to society and to the individual."

Fundamental rights can't be limited except under extraordinary circumstances and laws limiting them are presumed to be unconstitutional. In order for a law to be found constitutional, the state needs to show that the law serves a compelling purpose and that the law is necessary to achieve that compelling purpose.

The majority found that the state failed to make its case on both counts. Here's why:

1. excluding same-sex couples from "marriage" isn't necessary because letting us marry won't deprive opposite-sex couples of any rights. It also won't change the legal framework of marriage, because same-sex couples who marry will be subject to the same obligations imposed on heterosexual couples.
2. Retaining "marriage" for straights and giving "domestic partnerships" to gays will "impose appreciate harm on same-sex couples and their children, because denying such couples access to the familiar and highly favored designation of marriage is likely to cast doubt on whether the official family relationship of same-sex couples enjoys dignity equal to that of opposite-sex couples."
3. The widespread disparagement and discrimination gay people have faced makes it likely that excluding them from marriage will be construed as an official view that our relationships are less important than those of opposite-sex couples.
4. Excluding us from marriage may have the effect of perpetuating the premise that we are second-class citizens who may be treated differently from, and less favorably than, heterosexuals. That is unacceptable.

In other words, letting us marry won't hurt marriage, but preventing us from marrying will hurt us, even if the state gives us all the legal rights of marriage under another name, because the word itself matters.

As the court says, "[B]ecause of the long and celebrated history of the term "marriage" and the widespread understanding that this term describes a union unreservedly approved and favored by the community, there clearly is a considerable and undeniable symbolic importance to this designation." The connotation of "domestic partnership" is clearly different. The court again: "it is difficult to deny that the unfamiliarity of the term "domestic partnership" is likely, for a considerable period of time, to pose significant difficulties and complications for same-sex couples, and perhaps most poignantly for their children, that would not be presented if, like opposite-sex couples, same-sex couples were permitted access to the established and well-understood family relationship of marriage."

More money quotes:

Whether or not the name "marriage," in the abstract, is considered a core element of the state constitutional right to marry, one of the core elements of this fundamental right is the right of same-sex couples to have their official family relationship accorded the same dignity, respect, and stature as that accorded to all other officially recognized family relationships.

Accordingly, we conclude that the right to marry, as embodied in article I, sections 1 and 7 of the California Constitution, guarantees same-sex couples the same substantive constitutional rights as opposite sex couples to choose one's life partner and enter with that person into a committed, officially recognized, and protected family relationship that enjoys all of the constitutionally based incidents of marriage.

The Right to Equal Protection

While the "right to marry" ruling is going to get most of the press, the majority's equal protection ruling is as or more significant. For the first time ever, a state high court has ruled that discrimination on the basis of sexual orientation should be treated the same as discrimination on the basis of race, gender, or religion. Namely, it should be subject to strict scrutiny and any laws that draw distinctions based on sexual orientation should be struck down unless the state can show that they serve a compelling purpose and are necessary to achieving that purpose. Said the court,

Because sexual orientation, like gender, race, or religion, is a characteristic that frequently has been the basis for biased and improperly stereotypical treatment and that generally bears no relation to an individual's ability to perform or contribute to society, it is appropriate for courts to evaluate with great care and with considerable skepticism any statute that embodies such a classification.

This is huge, because it goes way beyond the specific issue of marriage. For the first time ever, a state supreme court has ruled that discrimination on the basis of sexual orientation is just as objectionable as discrimination on the basis of gender, race, or religion.

More money quotes:

Because a person's sexual orientation is so integral an aspect of one's identity, it is not appropriate to require a person to repudiate or change his or her sexual orientation in order to avoid discriminatory treatment.

Although the understanding of marriage as limited to a union of a man and a woman is undeniably the predominant one, if we have learned anything from the significant evolution in the prevailing societal views and official policies toward members of minority races and toward women over the past half-century, it is that even the most familiar and generally accepted of social practices and traditions often mask an unfairness and inequality that frequently is not recognized or appreciated by those not directly harmed by those practices or traditions..

There's a lot more in this decision, including a delightful section where the majority decision takes on and debunks a series of arguments about why same-sex couples shouldn't be permitted to marry, but I'll have to get to that later. Right now, I'm off to celebrate the decision by picking up my daughter from her play date. What could be more radical?