The news that U.S. Supreme Court Justice Ruth Bader Ginsburg is suffering from pancreatic cancer raises the theoretical possibility that if the next appointment to the Supreme Court isn't a woman, that institution will once again be all-male.

I say "theoretical" because it's difficult to imagine that, if Ginsburg is the next justice to leave the court, President Barack Obama would even consider nominating a man to replace her. And that is as it should be.

Affirmative action is a tricky issue for many reasons, one of which is that it comes in so many different varieties. At the extremes, you have, on the one hand, the view that precisely proportional representation in regard to certain characteristics ought to be maintained through selection quotas.

From this perspective, four or five of the nine Supreme Court justices ought to be women, and the nomination process should be dedicated to producing this result, by refusing to consider men at all until this proportion is reached and maintained.

At the other end of the spectrum you have the view that supposedly irrelevant characteristics such as gender should play no role whatsoever in the nomination process, which should be conducted strictly on the basis of what proponents of this position characterize as "merit." In this view, the nomination should always go to "the most qualified person," with the proviso that being a woman is by definition not the sort of thing that can ever count as a qualification for serving on the Supreme Court.

Both these views have the merit of vindicating a simple principle at the expense of everything else, which makes them intellectually attractive to a certain sort of person.

Many people, however, aren't willing to sign on to either of these views. Such people (I'm one of them) take the position that, while a proportional quota system in these sorts of contexts sacrifices too many other values, there's a point at which a lack of practical and symbolic diversity becomes so glaring that something like gender does in fact become a crucial qualification for a Supreme Court nominee.

Now that a full generation has passed during which nearly half of all law graduates have been women, it would be preposterous to return to a situation in which there isn't a single woman on the Supreme Court.

Whether we like it or not, it's an undeniable fact that a person's gender makes an enormous difference in regard to how he or she is both perceived and treated in society. Given this, it ought to be considered mandatory to have some minimal level of gender diversity on an institution as powerful as the Supreme Court.

While it's true that a man can with effort have some success in imagining what it's like to be a woman (and vice versa), in the end there's no substitute for firsthand experience.

And we shouldn't underestimate the symbolic importance of making sure places like the Supreme Court don't return to being the kind of places where it was so normal for everyone to be a man that it took literally centuries for people to become conscious this was the case.

One red herring we should avoid is the notion that it's important to nominate "the best qualified person" to any Supreme Court vacancy. Because the characteristics of good judges are both so relatively commonplace and difficult to measure, it's the case that at any one time there are literally thousands of people who are plausible candidates to serve on the Supreme Court. And it's basically absurd to imagine one could determine who the one best candidate out of this group is.

Since, at this point, roughly half of these fully qualified people are women, and since it's imperative to have women on the Supreme Court, Obama should consider only women to replace Ginsburg.

Paul Campos is a professor of law at the University of Colorado. He can be reached at paul.campos@colorado.edu.