BOSTON — As someone who makes a living telling people what she thinks, I am aware that opinion-mongering is a dicey business. Even the dictionary offers this slippery definition: "a belief or conclusion held with confidence but not substantiated by positive knowledge or proof."

Of course, it is not a problem if you are discussing cilantro or the Red Sox. It's more unsettling when you're talking about the law.

So when the Supreme Court ended with a bang, it left some queasiness behind. In the affirmative action case especially, there's been a good deal of conversation about the gap between Sandra Day O'Connor and Clarence Thomas.

These two justices are arguably the "affirmative action babies" of this court — the first woman and the second African-American. Each lived through an era when race or gender worked against them, and was picked for the court at a moment when race or gender worked for them. But they ended up with opposing opinions.

The woman who graduated from Stanford Law School a half-century ago and was offered a job only as a legal secretary wrote that affirmative action is good for the country. The African-American who graduated from Yale Law School and went on to success as a black conservative argued that it is bad for the "beneficiaries."

Observing this difference, Harvard law professor Laurence Tribe muses, "Justice O'Connor drew the lesson that even though she may have received a rare boost by virtue of being a woman, the opportunity to prove oneself is wide open and no stigma needs to result." But Justice Thomas? "It seems as though from Yale Law School to the present he has lived under some kind of doubt about who he is and why he is there and assumes that doubt is an inevitable consequence."

Not all, or even most, judicial opinions conjure up a judge's experience. But this odd couple left many asking: How much are they, or any of us, the products of our past? Is biography destiny? Or do we reshape our own biographies?

This is not just the kind of question about nature and nurture and free will you missed in Phil 101 or in Sunday school. For a long time, many believed that the best opinions on every subject were the products of a detached intellect. They believed justices should — and could — check their biographies at the courthouse door. They could adopt what philosopher Thomas Nagel described as the "view from nowhere."

Today, Americans are more likely to believe that everything from the political to the legal is personal. Every candidate now talks about his or her background. No judicial confirmation hearing would be complete without a life story. Indeed, part of the belief in diversity itself — on the bench or on the campus — comes from a belief in the importance of biography. We assume that in order to understand where leaders will take us, we have to know where they are coming from.

But individuals are far too complex to draw a predictable narrative line from background A to opinion B. One self-made man, for example, may conclude that we should all pick ourselves up by our bootstraps while another subsidizes bootstraps.

On the Supreme Court itself, Clarence Thomas and Antonin Scalia have little history in common, but they are joined at the head. Scalia and Anthony Kennedy, both born in 1936, both Roman Catholics, both Harvard Law School grads appointed by Ronald Reagan, couldn't have been further apart on the gay rights case. And Sandra O'Connor and Ruth Ginsburg, two brainy women of a certain generation, often take the same side on discrimination, but the Arizonan and the New Yorker part company on many issues from west and east.

It's hard to unravel our own biographies and beliefs. We need a good dose of self-knowledge, an ability to acknowledge experiences and reflect on their impact.

But then, of course, that's just my opinion.

Ellen Goodman's e-mail address is; Washington Post Writers Group