The Great Divide is a series about inequality.

Most recent discussion about economic inequality in the United States has focused on the top 1 percent of the nation’s income distribution, a group whose incomes average $1 million (with a bottom threshold of about $367,000). “We are the 99 percent,” declared the Occupy protesters, unexpectedly popularizing research findings by two economists, Thomas Piketty and Emmanuel Saez, that had previously drawn attention mainly from academics. But the gap between the 1 percent and the 99 percent is only half the story.

Granted, it’s an important half. Since 1979, the one-percenters have doubled their share of the nation’s collective income from about 10 percent to about 20 percent. And between 2009, when the Great Recession ended, and 2011, the one-percenters saw their average income rise by 11 percent even as the 99-percenters saw theirs fall slightly. Some recovery!

This dismal litany invites the conclusion that if we would just put a tight enough choke chain on the 1 percent, then we’d solve the problem of income inequality. But alas, that isn’t true, because it wouldn’t address the other half of the story: the rise of the educated class.

Since 1979 the income gap between people with college or graduate degrees and people whose education ended in high school has grown. Broadly speaking, this is a gap between working-class families in the middle 20 percent (with incomes roughly between $39,000 and $62,000) and affluent-to-rich families (say, the top 10 percent, with incomes exceeding $111,000). This skills-based gap is the inequality most Americans see in their everyday lives.

Conservatives don’t typically like to talk about income inequality. It stirs up uncomfortable questions about economic fairness. (That’s why as a candidate Mitt Romney told a TV interviewer that inequality was best discussed in “quiet rooms.”) On those rare occasions when conservatives do bring it up, it’s the skills-based gap that usually draws their attention, because it offers an opportunity to criticize our government-run system of public education and especially teachers’ unions.

Liberals resist talking about the skills-based gap because they don’t want to tell the working classes that they’re losing ground because they didn’t study hard enough. Liberals prefer to focus on the 1 percent-based gap. Conceiving of inequality as something caused by the very richest people has obvious political appeal, especially since (by definition) nearly all of us belong to the 99 percent. There’s also a pleasing simplicity to the causes of the growing gap between the 1 and the 99. There are only two, and both are familiar liberal targets: the rise of a deregulated financial sector and the erosion of accountability in compensating top executives outside finance. (The cohort most reflective of these trends is actually the top 0.1 percent, who make $1.6 million or more, but let’s not quibble.)

Both halves of the inequality story should command our attention, because both represent a dramatic reversal of economic trends that prevailed in the United States for most of the 20th century. From the 1930s through the 1970s the 1 percent saw its share of national income decline, while the “college premium” either fell or followed no clear up-or-down pattern over time.

At least some of the tools to restore these more egalitarian trends shouldn’t be divisive ideologically. Liberals and conservatives both recognize the benefits of preschool education, which President Obama has proposed making universally available. I’ve never met an affluent 4-year-old who wasn’t enrolled in preschool, but nationwide about one-third of kids that age aren’t.

Another reform both conservatives and liberals have supported — though at different times — is withholding federal aid from colleges and universities that can’t control tuition increases. Mr. Obama proposed it in his last two State of the Union addresses; House Speaker John A. Boehner was a sponsor of a bill to do the same in 2003.

THERE is also more bipartisan support than you might suppose for restricting some of the Wall Street excesses that enrich the 1 percent. The impetus to do so isn’t inequality so much as fear that an out-of-control banking sector will once again create economic crisis and compel Congress to bail out the big banks. Congressional Republicans have been blocking proper implementation of the Dodd-Frank financial reforms, but a growing chorus of conservative voices, including the columnist George F. Will, the former Utah governor Jon M. Huntsman Jr. and Richard W. Fisher, president of the Federal Reserve Bank of Dallas, favor breaking up the big banks. Senators David Vitter, Republican of Louisiana, and Sherrod Brown, Democrat of Ohio, have sponsored a bill to require the largest banks to hold more capital reserves, or become smaller.

One reason the left plays down the growing skills-based gap is that it accepts at face value the conservative claim that educational failure is its root cause. But the decline of labor unions is just as important. At one time union membership was highly effective at reducing or eliminating the wage gap between college and high school graduates. That’s much less true today. Only about 7 percent of the private-sector labor force is covered by union contracts, about the same proportion as before the New Deal. Six decades ago it was nearly 40 percent.

The decline of labor unions is what connects the skills-based gap to the 1 percent-based gap. Although conservatives often insist that the 1 percent’s richesse doesn’t come out of the pockets of the 99 percent, that assertion ignores the fact that labor’s share of gross domestic product is shrinking while capital’s share is growing. Since 1979, except for a brief period during the tech boom of the late 1990s, labor’s share of corporate income has fallen. Pension funds have blurred somewhat the venerable distinction between capital and labor. But that’s easy to exaggerate, since only about one-sixth of all households own stocks whose value exceeds $7,000. According to the left-leaning Economic Policy Institute, the G.D.P. shift from labor to capital explains fully one-third of the 1 percent’s run-up in its share of national income. It couldn’t have happened if private-sector unionism had remained strong.

Reviving labor unions is, sadly, anathema to the right; even many mainstream liberals resist the idea. But if economic growth depends on rewarding effort, we should all worry that the middle classes aren’t getting pay increases commensurate with the wealth they create for their bosses. Bosses aren’t going to fix this problem. That’s the job of unions, and finding ways to rebuild them is liberalism’s most challenging task. A bipartisan effort to revive the labor movement is hardly likely, but halting inequality’s growth will depend, at the very least, on liberals and conservatives better understanding each other’s definition of where the problem lies.

Timothy Noah is the author of “The Great Divergence: America’s Growing Inequality Crisis And What We Can Do About It.”