Libertarians, socialists, tech founders, feminists and religious reformers have all championed some version of a basic income, often meaning quite different things by it. Before weighing the arguments, it helps to pin down what is being proposed and how it differs from its close cousins.

Five features

Researchers usually describe a full basic income by five features. It is paid in cash, not in food stamps or housing vouchers, so recipients decide how to use it. It is periodic, arriving every month or year rather than once. It is individual: each adult receives a payment in their own name, rather than one check going to the head of a household. It is universal, going to rich and poor alike. And it is unconditional, with no duty to work or look for work. Remove any of these and you have something else.

The individual feature matters more than it first seems. When support goes to a household, it usually lands with whoever earns most, often a husband. A payment in each person's name gives a spouse with no earnings some money of their own.

Full and partial

A second question is size. A full basic income would be large enough to live on modestly without other earnings. A partial basic income is a payment too small to live on alone, meant to be topped up by work, savings or other benefits. Most serious proposals in rich countries today are partial, partly because a full one would be very expensive, and partly because supporters want to keep extra aid for disabled people and others with high costs.

The negative income tax

A close relative is the negative income tax. Under it, people below an income threshold receive money from the tax system instead of paying into it. A negative income tax pays the most to people with no earnings and then reduces the payment gradually as earnings rise, so it phases out at some higher income. Suppose the guarantee is 10,000 dollars and the phase out rate is 50 percent. Someone who earns nothing gets 10,000. Someone who earns 8,000 keeps it and gets 6,000 more, for 14,000 in all. At 20,000 in earnings, the payment reaches zero.

Economists point out that a basic income paired with a tax that claws it back can produce the same final incomes as a negative income tax, because taxes can recover it from higher earners. The difference lies in how the money moves and how it feels. With a basic income, everyone gets the check first and the better off pay it back through taxes. With a negative income tax, only those under the line receive anything, usually after filing a return. Payment up front helps people whose income swings from month to month, while the tax route looks cheaper on paper, because the gross sum spent is smaller.

Conditional cousins

Other designs keep a condition. Conditional cash transfers pay poor families on condition that children attend school and get health checkups. Mexico's Progresa, launched in 1997, and Brazil's Bolsa Família, launched in 2003, became the models, and dozens of countries copied them. They are targeted at the poor, so they are neither universal nor unconditional.

The British economist Anthony Atkinson proposed in 1996 what he called a participation income. A participation income would go to everyone who contributes to society in some recognized way, whether through paid work, caring for children or elderly relatives, study, volunteering or job seeking. Atkinson thought such a broad condition would win more public support.

A different idea gives one large sum instead of a stream. In The Stakeholder Society (1999), the law professors Bruce Ackerman and Anne Alstott proposed giving every young adult 80,000 dollars at age 21. A stakeholder grant is a single large payment at the start of adult life, which supporters say lets young people pay for training, start a business or put down a deposit on a home. Critics fear some would spend it fast and be left with nothing.

What a pilot usually tests

Almost every "basic income experiment" drops at least one of the five features. Most select a sample of people, often poor ones, rather than paying a whole community; most last only a few years; and almost none raise the taxes that a real program would need. Each study tests a piece of the idea, and readers should ask which piece.

Worked example: sorting four proposals

A city council hears four plans. Plan A pays 300 dollars a month to every adult resident. Plan B pays 1,000 dollars a month to low-income families whose children attend school on at least 85 percent of days. Plan C tops up the earnings of anyone earning under 30,000 dollars a year, shrinking the top up as earnings rise. Plan D pays 500 dollars a month to adults who work, study, volunteer or care for a relative.

Plan A is a partial basic income: universal, individual and unconditional, but too small to live on. Plan B is a conditional cash transfer. Plan C works like a negative income tax. Plan D is a participation income. Naming them correctly does not settle which is best, but it keeps the debate honest, since evidence about Plan B says little about Plan A.