A society is embodied most visibly in public institutions -- public schools, public libraries, public transportation, public hospitals, public parks, public museums, public recreation, public universities, and so on.
But much of what's called "public" today is increasingly private. Tolls are rising on public highways and public bridges, as are tuitions at so-called public universities, and admission fees at public parks and public museums.
Much of the rest of what's considered "public" has become so shoddy that those who can afford to do so find private alternatives.
As public schools deteriorate, the upper middle class and wealthy send their kids to private ones. As public pools and playgrounds decay, the better-off buy memberships in private tennis and swimming clubs. As public hospitals decline, they pay premium rates for private care.
Gated communities and office parks now come with their own manicured lawns and walkways, security guards, and backup power systems.
Why the decline of public institutions? The financial squeeze on government at all levels since 2008 explains only part of it.
The slide really started more than three decades ago, with so-called "tax revolts" by a middle class whose earnings had stopped advancing even though the economy continued to grow. Most families still wanted good public services but could no longer afford the tab.
When almost all the gains from growth started going to the top, the better-off began shifting to private institutions and withdrew political support for public ones -- including their tax payments. This created a vicious cycle of diminishing public revenues and deteriorating quality, spurring more flight from public institutions. Tax revenues from corporations also dropped as big companies went global -- keeping their profits overseas and their tax bills to a minimum.
But that's not the whole story. America no longer values public goods as we did decades ago.
The great expansion of public institutions in America began in the early years of the 20th century, when progressive reformers championed the idea that we all benefit from public goods. Excellent schools, roads, parks, playgrounds and transit systems would knit the new industrial society together, create better citizens, and generate widespread prosperity. Education, for example, was less a personal investment than a public good -- improving the entire community and ultimately the nation.
This logic was expanded upon in subsequent decades -- through the Great Depression, World War II and the Cold War. The "Greatest Generation" was bound together by mutual needs and common threats. It invested in strong public institutions as bulwarks against, in turn, mass poverty, fascism and then communism.
Yet in recent years the idea of the public good has faded. "We're all in it together" has been replaced by "You're on your own" -- as global capital outsources American jobs abroad, the very rich take home an almost unprecedented portion of total earnings, and a new wave of immigrants is described by demagogues as "them."
Not even Democrats still use the phrase "the public good." Public goods are now, at best, "public investments." Public institutions have morphed into "public-private partnerships" or, for Republicans, simply "vouchers."
Mitt Romney speaks derisively of what he terms the Democrats' "entitlement" society, in contrast to his "opportunity" society. At least he still envisions a society. But he hasn't explained how ordinary Americans will be able to take advantage of good opportunities without good public schools, affordable higher education, good roads and adequate health care.
His "entitlements" are mostly a mirage anyway. Medicare is the only entitlement growing faster than the gross domestic product, but that's because the costs of health care are growing faster than the economy. Social Security hasn't contributed to the budget deficit; it's had surpluses for years.
Other safety nets are in tatters. Unemployment insurance reaches just 40 percent of the jobless these days.
Outside of defense, domestic discretionary spending is down sharply as a percent of the economy. With declining state and local spending, total public spending on education, infrastructure and basic research has dropped from 12 percent of GDP in the 1970s to less than 3 percent by 2011.
Only in one respect is Mr. Romney right. America has created a whopping entitlement for the biggest Wall Street banks and their top executives, who, unlike most of the rest of us, are no longer allowed to fail.
We're losing public goods available to all, supported by the tax payments of all and especially the better off. In their place we have private goods available to the very rich, supported by the rest of us.
Even Lady Thatcher would have been appalled.
Robert Reich, former U.S. Secretary of Labor, is professor of public policy at the University of California at Berkeley and the author of "Aftershock: The Next Economy and America's Future." He blogs at www.robertreich.org.