ASHINGTON, June 24 — As they approached the University of Michigan affirmative action cases, Justice Sandra Day O'Connor and Justice Clarence Thomas appeared to be responding to completely different cues.

For Justice O'Connor, the broad societal consensus in favor of affirmative action in higher education, as reflected in an outpouring of briefs on Michigan's behalf from many of the country's most prominent institutions, was clearly critical to her conclusion that the law school's "holistic" and "individualized" consideration of race was not only acceptable but also, at least for the next 25 years, necessary to achieve a more equal society.

Justice Thomas, whose impassioned 31-page dissenting opinion in the law school case was almost precisely the length of Justice O'Connor's majority opinion, took as his text not the briefs but his own life story.

"I must contest the notion that the law school's discrimination benefits those admitted as a result of it," he said at the start of a remarkable series of paragraphs, most without footnotes, statistics or outside references, about the pain and stigma suffered by recipients of affirmative action.

Justice O'Connor observed in her opinion that "context matters when reviewing race-based governmental action under the Equal Protection Clause." The context provided by the briefs from Fortune 500 companies, senior military officers, and colleges and universities big and small, public and private, quite clearly won the day for Michigan.

Context always matters at the court, though it is not always acknowledged by justices who, unlike Justice O'Connor, prefer to deal in absolutes. What the rulings demonstrated was not simply the power of context but the importance of the different contexts from which the justices view the cases that bring them face to face with society's most profound disputes.

For Justices O'Connor and Thomas, their opposite starting points as well as their opposite conclusions make the law school case, Grutter v. Bollinger, a useful window into the styles of two of the court's most distinctive members.

In her new book "The Majesty of the Law," a collection of essays published the week after the Michigan cases were argued in April, Justice O'Connor wrote that "courts, in particular, are mainly reactive institutions." Noting that "change comes principally from attitudinal shifts in the population at large," she said that "rare indeed is the legal victory — in court or legislature — that is not a careful byproduct of an emerging social consensus."

The challenge facing the University of Michigan and its defenders was to demonstrate such a consensus on behalf of affirmative action, and they met the challenge brilliantly. The briefs, from which Justice O'Connor quoted extensively, provided the context for concluding that affirmative action's benefits "are not theoretical but real, as major American businesses have made clear," she said at one point with a nod to two of the corporate briefs.

Another part of the context for Justice O'Connor was the 25-year-old opinion in the Bakke case by an admired mentor, Justice Lewis F. Powell Jr. Justice Powell's solitary opinion establishing diversity as a "compelling state interest" justifying affirmative action in admissions had been on shaky ground before five justices embraced it on Monday.

At the heart of Justice Thomas's dissenting opinion was a highly personal critique of affirmative action, which he called the "cruel farce of racial discrimination."

"The law school tantalizes unprepared students with the promise of a University of Michigan degree and all of the opportunities that it offers," he said, adding, "These overmatched students take the bait, only to find that they cannot succeed in the cauldron of competition."

Justice Thomas, himself a beneficiary of affirmative action at Yale Law School, compiled a respectable record at what is arguably the country's most elite law school. So his opinion reflected not objective failure so much as a lifelong struggle with the ambiguous position in which beneficiaries of affirmative action — "test subjects," as he put it — often found themselves as elite institutions felt their way, sometimes clumsily, toward a more inclusive identity in the cauldron of the early 1970's.