PRINCETON • Inequality has been named as a culprit in the populist incursions of 2016 and 2017.

But what is inequality, and what role does it play in inhibiting or encouraging growth, or in undermining democracy? Does inequality kill, say, by driving people to suicide or to "deaths of despair"? Or is inequality a necessary evil that we must tolerate at certain levels?

These are questions I am often asked. But, truth be told, none of them is particularly helpful, answerable, or even well posed.

Inequality is not so much a cause of economic, political, and social processes as a consequence. Some of these processes are good, some are bad, and some are very bad indeed. Only by sorting the good from the bad (and the very bad) can we understand inequality and what to do about it.

Moreover, inequality is not the same thing as unfairness; and, to my mind, it is the latter that has incited so much political turmoil in the rich world today. Some of the processes that generate inequality are widely seen as fair. But others are deeply and obviously unfair, and have become a legitimate source of anger and disaffection.

In the case of the former, it is hard to object to innovators getting rich by introducing products or services that benefit all mankind. Some of the greatest inequalities today are a consequence of industrial and health revolutions that began around 1750. Originally, these processes benefited just a few countries in north-west Europe. But they have since improved living conditions and health outcomes for billions of people worldwide. The inequalities stemming from these advances - both within and between countries - are beneficial and fair, and a key feature of progress generally.

On the other hand, getting rich by bribing the state for special favours is clearly unfair, and rightly resented. Many in the United States - more so than in Europe - automatically regard capitalist or market outcomes as fair, and government action as arbitrary and unfair. They object to government or university-sponsored programmes that seem to favour particular groups, such as minorities or immigrants.

This helps to explain why many white working-class Americans have turned against the Democratic Party, which they view as the party of minorities, immigrants and educated elites. But another reason for growing public discontent is that median real (inflation-adjusted) wages in the US have stagnated over the past 50 years.

There are two different explanations for the divergence between median and top incomes, and it matters a great deal which one is correct. The first attributes it to impersonal and unstoppable processes such as globalisation and technological innovation, which have devalued low-skill labour and favoured the well educated.

The second explanation is more sinister. It holds that median-income stagnation is the direct result of rising incomes and wealth at the top. In this account, the rich are getting richer at the expense of everyone else.

Recent research suggests there is some truth to the second story, at least in the United States. Although globalisation and technological change have disrupted traditional work arrangements, both processes have the potential to benefit everyone. The fact that they have not suggests the wealthy have captured the benefits for themselves. It will take much more work to determine which policies and processes are holding down middle-and working-class wages, and by how much, but what follows is a preliminary list.

WHAT'S KEEPING WORKERS' WAGES DOWN

First, healthcare financing is having a disastrous effect on wages. Because most Americans' health insurance is provided by their employers, workers' wages are essentially paying for profits and high salaries in the medical industry. Every year, the US wastes a trillion dollars (S$1.35 trillion) - about US$8,000 per family - more than other rich countries on excessive healthcare costs, and has worse health outcomes than nearly all of them. Any one of several European financing alternatives could recoup those funds, but adopting any of them would trigger fierce resistance from those now profiting from the status quo.

A related problem is increasing market consolidation in many sectors of the economy. As a result of hospital mergers, for example, hospital prices have risen rapidly, but hospital wages have not, despite a decades-long shortage of nurses.

Increasing market concentration is probably a factor underpinning slow productivity growth, too. After all, it is easier to reap profits through rent-seeking and monopolisation than through innovation and investment.

Another problem is that the US federal minimum wage - at US$7.25 per hour - has not risen since July 2009. Despite public support, raising the minimum wage is always hard, owing to the disproportionate influence that rich firms and donors have in Congress.

Making matters worse, over 20 per cent of workers are bound by non-compete clauses, which reduce workers' bargaining power - and thus their wages. Similarly, 28 US states have now enacted so-called "right-to-work" laws, which forbid collective-bargaining arrangements that would require workers either to join unions or pay union dues. As a result, disputes between businesses and consumers or workers are increasingly settled out of court through arbitration - a process that overwhelmingly favours businesses.

Yet another problem is outsourcing, not just abroad, but also within the US, where businesses are increasingly replacing salaried or full-time workers with independent contractors. The food servers, janitors and maintenance workers who used to be a part of successful companies are now working for entities with names like AAA-Service Corporation. These companies operate in a highly competitive low-wage industry, and provide few or no benefits and little opportunity for advancement.

The earned income tax credit has provided a boost in living standards for many low-paid US workers. But, because it is available only to those who work, it puts downward pressure on wages in a way that unconditional benefits, like a basic-income grant, would not.

Unskilled immigration also poses a problem for wages, though this is controversial. It is often said that immigrants take jobs that Americans do not want. But such statements are meaningless without some reference to wages.

It hard to believe that low-skilled Americans' wages would have remained as low as they did in the absence of inflows of unskilled immigrants. As the economist Dani Rodrik pointed out 20 years ago, globalisation makes demand for labour more elastic. So, even if globalisation does not reduce wages directly, it makes it harder for workers to get a pay raise.

Another structural problem is that the stock market rewards not just innovation but also redistribution from labour to capital.

This is reflected in the share of profits relative to GDP, which has grown from 20 per cent to 25 per cent over the same period that median wages have stagnated. The increase would be even higher if executive salaries were counted as profits rather than wages.

The final problem on our preliminary list is political. We have entered a period of regulatory bonfires. The Consumer Financial Protection Bureau, despite having uncovered major scandals, is under threat, as is the 2010 Dodd-Frank legislation, which introduced measures to prevent another financial crisis. Moreover, President Donald Trump has indicated that he wants to eliminate a rule requiring money managers to act in their clients' best interest. All of the deregulatory "reforms" being proposed will benefit capital at the expense of workers and consumers.

The same is true of Supreme Court rulings in recent years. The court's decision in Citizens United v. FEC, for example, gave rich Americans and even corporations the ability to spend almost unlimited sums to support candidates and engineer legislative and regulatory outcomes that work in their favour.

If this account of stagnant median wages and rising top wages is correct, then there may be a silver lining to our era of inequality, because it means that the US' dysfunctional labour market is not an irremediable consequence of unstoppable processes such as globalisation and technological change.

Broadly shared progress can be achieved with policies that are designed specifically to benefit consumers and workers. And such policies need not even include redistributive taxation, which many workers oppose. Rather, they can focus on ways to encourage competition and discourage rent-seeking.

With the right policies, capitalist democracy can work better for everyone, not just for the wealthy. We do not need to abolish capitalism or selectively nationalise the means of production. But we do need to put the power of competition back in the service of the middle and working classes.

PROJECT SYNDICATE

•Angus Deaton, the 2015 Nobel laureate in economics, is presidential professor of economics at the University of Southern California and professor of economics and international affairs at Princeton University's Woodrow Wilson School of Public and International Affairs.