It was not the type of question that one usually hears from lawyers in federal court.
“What does it mean,” Theodore B. Olson asked his client, Kristin M. Perry, “to be a lesbian?”
Mr. Olson’s question came during one of several attention-grabbing moments on the first day of the trial here on the constitutionality of Proposition 8, California’s voter-approved ban on same-sex marriage. It is a case that is expected to feature three weeks of evidence, experts and — if Monday was an indication — emotionally charged testimony on everything from the nature of gay sexuality to the nature of a romantic same-sex marriage proposal.
Ms. Perry, a 45-year-old child services professional who brought the case with her partner, Sandra B. Stier, 47, and a male couple, recounted how she had slowly fallen in love with Ms. Stier.
“I remember thinking that she was the sparkliest person I’d ever met,” Ms. Perry said, drawing giggles from the packed courtroom. When she told Ms. Stier of her feelings, she said, “she told me she loved me, too.” Ms. Perry proposed marriage in 2003, although same-sex marriage was illegal then in California and every other state.
“She looked really happy,” Ms. Perry recalled, “and then she looked really confused.”
Such human touches, of course, are part of the legal strategy Mr. Olson and his law partner on this case, David Boies, who have cast their efforts to overturn Proposition 8 as a seminal civil rights struggle.
“That is exactly why we have courts, why we have the Constitution and why we have the 14th Amendment,” Mr. Olson said in his opening statement, adding that while some groups “may not be the most popular people,” the court still should uphold their rights. “That is why we are here today,” he said.
Supporters of Proposition 8, who were granted legal status to defend the ban in court, were quick to disagree. Their lawyers sharply questioned early witnesses about whether lessons on same-sex marriage belong in elementary school.
“Do you think first- and second-graders should be taught about sex in public schools?” Brian Raum, a lawyer for the defendants, asked Paul T. Katami, who is a plaintiff, as is his partner, Jeffrey J. Zarrillo.
Mr. Katami responded that it depended “on how it’s being taught,” before adding “I do know that children are growing up a lot faster.”
The defendants also showed clips from the campaign for Proposition 8, which passed in 2008 with 52 percent of the vote. Mr. Raum asked Mr. Katami why he found one slogan of the “Yes on 8” campaign — “Protect Your Children” — offensive.
“I have a problem with the verbiage of ‘protect your children’ because it insinuates that they have to protect them from something that’s going to harm them,” Mr. Katami said.
Judge Vaughn R. Walker of Federal District Court, who is hearing the case, repeatedly interrupted the opening statements of Mr. Olson and the lead defense counsel, Charles J. Cooper, admonishing the lawyers to provide hard evidence — not just rhetoric.
Both parried with the judge, with Mr. Olson promising expert testimony showing “the grievous harm” caused to gay men and lesbians not allowed to marry, and Mr. Cooper countering that the defense would show that allowing same-sex marriage would undermine traditional marriage and urging “special regard for this venerable institution.”