The Massachusetts high court yesterday issued a sweeping defense of same-sex marriage and flatly rejected as unconstitutional a proposed compromise bill on civil unions.

The 4-3 decision by the Supreme Judicial Court (SJC), which clarified its historic November ruling, paved the way for same-sex marriages to begin in Massachusetts on May 17.

“The dissimilitude between the terms ‘civil union’ and ‘civil marriage’ is not innocuous; it is a considered choice of language that reflects a demonstrable assigning of same-sex, largely homosexual, couples to second-class status,” the justices wrote.

In November, the SJC gave the state Legislature 180 days to grant same-sex couples the right to wed.

The state Senate responded by asking the court to examine a bill which would have afforded same-sex couples the same benefits and protections of marriage, but without the moniker.

Yesterday, the SJC said the bill didn’t go far enough, and explicitly rejected the state Senate’s proposal of civil unions.

“The answer to the question is ‘No,’” they said.

Opponents of the court’s decision were left with little recourse to prevent what would be the nation’s first gay marriage law. A convention of state legislators scheduled to convene next Wednesday could attempt to amend the constitution to define marriage as a union between a man and a woman, but the amendment could not be posed to voters until 2006 at the earliest.

“There’s literally nothing—short of a meteor, I suppose—that could get in the way of implementing gay marriage in this state on May 17,” Tyler Professor of Constitutional Law Laurence H. Tribe ’62 said in the wake of yesterday’s decision.

Tribe last month authored a friend-of-the-court brief signed by 90 law professors from around the country, including 18 from Harvard Law School, urging the court to strengthen its November ruling with explicit support for same-sex marriage.

State and national politicians from both major parties decried the court’s decision yesterday.

Leading Democratic presidential candidate Sen. John F. Kerry, D-Mass., said in a statement that he supported full rights for gay couples but not marriage.

“I believe the right answer is civil unions,” he said. “I oppose gay marriage and disagree with the Massachusetts Court’s decision.”

Kerry’s opponents in the Democratic primary have previously issued similar opinions.

Adam P. Schneider ’07, public relations chair for the Bisexual, Gay, Lesbian, Transgender and Straight Alliance, expressed concern about politicians who have opposed gay marriage.