Yesterday I introduced the issue of how the Supreme Court treats its past decisions. I mentioned a few possible explanations for why a justice might uphold a constitutional decision even if she thinks it’s wrong, and I paid special attention to the idea of judicial impersonality. A commitment to past decisions elevates the work of the court above the inclinations of the individual justice. The law remains stable even as judges come and go.

But the Supreme Court’s commitment to the past isn’t absolute. It isn’t, to use a phrase the court sometimes invokes, “an inexorable command.” Everybody agrees that some mistakes need to be corrected and that some decisions need to be overruled. The question is which ones. Was the court justified in 2010 when it expanded the protection of speech by corporations and labor unions, or should it have stood by its past decisions taking a more restrictive approach — even if a majority of justices thought those decisions were wrong? Should the court reconsider its decisions involving the funding of public-sector unions? What about its decisions involving states’ authority to tax out-of-state retailers? The list goes on and on, and working through the resulting tension is a major theme of my book, “Settled Versus Right.”

Let’s assume we all agree that decisions should be overruled if they’re deeply problematic. We still need to figure out what makes for a deeply problematic decision. And that creates serious challenges in developing a consistent approach to precedent.

To see why, start with the question of which factors the Supreme Court should consider when it’s interpreting the Constitution. Should it emphasize the Constitution’s original meaning? If so, why? To respect the will of the people, or to limit the justices’ discretion, or for some other reason? Or should the court look at the results of a law in determining whether it’s constitutional? If so, should the justices focus on policy outcomes, or contemporary ideas about justice and fairness, or something else?

These are some of the big questions in constitutional law. They go a long way toward shaping the debates between those who would interpret the Constitution according to its original meaning and those who would interpret it as a living document that evolves as values and attitudes change. One reason we’re not surprised when the Supreme Court issues a divided opinion on a controversial issue is that we know the justices are looking for different things.

Those same disagreements can affect the choice between overruling a past decision and upholding the decision for the sake of leaving things settled. Let’s say a Supreme Court justice believes that contemporary moral values are relevant to whether laws are struck down as constitutional. We might also expect him to conclude that past decisions are most problematic when they’re out of step with those values. But what if his ideas about constitutional law are different? What if he thinks the Constitution should be interpreted in light of its original meaning? Now he’s more likely to conclude that past decisions are most problematic when they play down or disregard the Constitution’s original meaning in favor of other considerations.

These examples are just rough sketches, but they suggest a broader point. The same factors that lead a Supreme Court justice to think a past decision is misguided can lead him to think the decision reflects the type of harmful mistake that needs to be corrected right away. Just as we’re not surprised when the justices split over new constitutional disputes, we shouldn’t be surprised when they split, for essentially the same reasons, over the treatment of past decisions.

This doesn’t mean the justices are being unprincipled. It just means they’re applying different principles, which lead to different conclusions about whether past decisions should stay or go.

That, I think, is a problem. It’s not a problem in the sense that the sky will fall or the Constitution will crumble. It’s more like a lost opportunity. By committing themselves to the court’s past decisions even when they’re flawed, Supreme Court justices help to make the institution more important than the individuals who comprise it. The court’s past decisions serve as a bridge across time that connects justices who are inclined to view the Constitution differently. But that can’t happen if the question whether to overrule a prior decision collapses into whether today’s justices disagree with the decision’s interpretive approach.

The upshot is that we need to think about precedent against a backdrop of disagreement among the justices. I’ll explain more about what that means in tomorrow’s post.