The venue, gay-friendly San Francisco, may at first glance seem predictable for a legal challenge that may lead to the legalisation of gay marriage in America. But nothing else about the trial of Perry v Schwarzenegger, which began on Monday January 11th, fits stereotypes. Pitting both a male and female gay couple (including Kristin Perry) against the state of California (nominally represented by its governor, Arnold Schwarzenegger), it is a federal review of whether Proposition 8, a Californian voter initiative of 2008 that outlawed gay marriage in the state, is constitutional.

Whatever the outcome, the case is likely to go to appeal and come before the Supreme Court. But first the trial will do two things: it will establish, for the first time, a body of evidence, through expert testimony, that appelate courts can use to evaluate the claims by supporters and opponents of gay marriage. And it will blur the existing partisan divide on the issue between conservatives and liberals.

This is thanks to the unusual pairing of lawyers who are arguing in favour of gay marriage for the plaintiffs. David Boies, a well-known liberal who litigated for Al Gore in his 2000 court fight against George Bush over the presidency, is an unsurprising choice. But his partner, Theodore Olson, is a prominent conservative and was Mr Boies’s courtroom adversary in 2000. Now he has teamed up with Mr Boies to argue for legalising gay marriage based on what he considers an arch-conservative interpretation of the constitution.

Read the rest of The Economist article here.