On Wednesday, President Obama called on Americans to “expand our moral imaginations, to listen to each other more carefully, to sharpen our instincts for empathy, and remind ourselves of all the ways our hopes and dreams are bound together.” Those were beautiful words; they spoke to our desire for reconciliation.

But the truth is that we are a deeply divided nation and are likely to remain one for a long time. By all means, let’s listen to each other more carefully; but what we’ll discover, I fear, is how far apart we are. For the great divide in our politics isn’t really about pragmatic issues, about which policies work best; it’s about differences in those very moral imaginations Mr. Obama urges us to expand, about divergent beliefs over what constitutes justice.

And the real challenge we face is not how to resolve our differences — something that won’t happen any time soon — but how to keep the expression of those differences within bounds.

What are the differences I’m talking about?

One side of American politics considers the modern welfare state — a private-enterprise economy, but one in which society’s winners are taxed to pay for a social safety net — morally superior to the capitalism red in tooth and claw we had before the New Deal. It’s only right, this side believes, for the affluent to help the less fortunate.

The other side believes that people have a right to keep what they earn, and that taxing them to support others, no matter how needy, amounts to theft. That’s what lies behind the modern right’s fondness for violent rhetoric: many activists on the right really do see taxes and regulation as tyrannical impositions on their liberty.

There’s no middle ground between these views. One side saw health reform, with its subsidized extension of coverage to the uninsured, as fulfilling a moral imperative: wealthy nations, it believed, have an obligation to provide all their citizens with essential care. The other side saw the same reform as a moral outrage, an assault on the right of Americans to spend their money as they choose.

This deep divide in American political morality — for that’s what it amounts to — is a relatively recent development. Commentators who pine for the days of civility and bipartisanship are, whether they realize it or not, pining for the days when the Republican Party accepted the legitimacy of the welfare state, and was even willing to contemplate expanding it. As many analysts have noted, the Obama health reform — whose passage was met with vandalism and death threats against members of Congress — was modeled on Republican plans from the 1990s.

But that was then. Today’s G.O.P. sees much of what the modern federal government does as illegitimate; today’s Democratic Party does not. When people talk about partisan differences, they often seem to be implying that these differences are petty, matters that could be resolved with a bit of good will. But what we’re talking about here is a fundamental disagreement about the proper role of government.

Regular readers know which side of that divide I’m on. In future columns I will no doubt spend a lot of time pointing out the hypocrisy and logical fallacies of the “I earned it and I have the right to keep it” crowd. And I’ll also have a lot to say about how far we really are from being a society of equal opportunity, in which success depends solely on one’s own efforts.

But the question for now is what we can agree on given this deep national divide.

In a way, politics as a whole now resembles the longstanding politics of abortion — a subject that puts fundamental values at odds, in which each side believes that the other side is morally in the wrong. Almost 38 years have passed since Roe v. Wade, and this dispute is no closer to resolution.

Yet we have, for the most part, managed to agree on certain ground rules in the abortion controversy: it’s acceptable to express your opinion and to criticize the other side, but it’s not acceptable either to engage in violence or to encourage others to do so.

What we need now is an extension of those ground rules to the wider national debate.

Right now, each side in that debate passionately believes that the other side is wrong. And it’s all right for them to say that. What’s not acceptable is the kind of violence and eliminationist rhetoric encouraging violence that has become all too common these past two years.

It’s not enough to appeal to the better angels of our nature. We need to have leaders of both parties — or Mr. Obama alone if necessary — declare that both violence and any language hinting at the acceptability of violence are out of bounds. We all want reconciliation, but the road to that goal begins with an agreement that our differences will be settled by the rule of law.