I met Matt Wage in 2009 when he took my Practical Ethics class at Princeton University. In the readings relating to global poverty and what we ought to be doing about it, he found an estimate of how much it costs to save the life of one of the millions of children who die each year from diseases that we can prevent or cure. This led him to calculate how many lives he could save, over his lifetime, assuming he earned an average income and donated 10 percent of it to a highly effective organization, such as one providing families with bed nets to prevent malaria, a major killer of children. He discovered that he could, with that level of donation, save about one hundred lives. He thought to himself, “Suppose you see a burning building, and you run through the flames and kick a door open, and let one hundred people out. That would be the greatest moment in your life. And I could do as much good as that!”

Two years later Wage graduated, receiving the Philosophy Department’s prize for the best senior thesis of the year. He was accepted by the University of Oxford for postgraduate study. Many students who major in philosophy dream of an opportunity like that—I know I did—but by then Wage had done a lot of thinking about what career would do the most good. Over many discussions with others, he came to a very different choice: he took a job on Wall Street, working for an arbitrage trading firm. On a higher income, he would be able to give much more, both as a percentage and in dollars, than 10 percent of a professor’s income. One year after graduating, Wage was donating a six-figure sum—roughly half his annual earnings—to highly effective charities. He was on the way to saving a hundred lives, not over his entire career but within the first year or two of his working life and every year thereafter.

A minimally acceptable ethical life involves using a substantial part of one’s spare resources to make the world a better place.

Wage is part of an exciting new movement: effective altruism. At universities from Oxford to Harvard and the University of Washington, from Bayreuth in Germany to Brisbane in Australia, effective altruism organizations are forming. Effective altruists are engaging in lively discussions on social media and websites, and their ideas are being examined in the New York Times, the Washington Post, and even the Wall Street Journal. Philosophy, and more specifically practical ethics, has played an important role in effective altruism’s development, and effective altruism shows that philosophy is returning to its Socratic role of challenging our ideas about what it is to live an ethical life. In doing so, philosophy has demonstrated its ability to transform, sometimes quite dramatically, the lives of those who study it. Moreover, it is a transformation that, I believe, should be welcomed because it makes the world a better place.

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Effective altruism is based on a very simple idea: we should do the most good we can. Obeying the usual rules about not stealing, cheating, hurting, and killing is not enough, or at least not enough for those of us who have the good fortune to live in material comfort, who can feed, house, and clothe ourselves and our families and still have money or time to spare. Living a minimally acceptable ethical life involves using a substantial part of our spare resources to make the world a better place. Living a fully ethical life involves doing the most good we can.

Most effective altruists are millennials—members of the first generation to have come of age in the new millennium. They are pragmatic realists, not saints, so very few claim to live a fully ethical life. Most of them are somewhere on the continuum between a minimally acceptable ethical life and a fully ethical life. That doesn’t mean they go about feeling guilty because they are not morally perfect. Effective altruists don’t see a lot of point in feeling guilty. They prefer to focus on the good they are doing. Some of them are content to know they are doing something significant to make the world a better place. Many of them like to challenge themselves to do a little better this year than last year.

Effective altruism is notable from several perspectives. First, and most important, it is making a difference to the world. Philanthropy is a very large industry. In the United States alone there are almost one million charities, receiving a total of approximately $200 billion a year, with an additional $100 billion going to religious congregations. A small number of these charities are outright frauds, but a much bigger problem is that very few of them are sufficiently transparent to allow donors to judge whether they are really doing good. Most of that $200 billion is given on the basis of emotional responses to images of the people, animals, or forests that the charity is helping. Effective altruism seeks to change that by providing incentives for charities to demonstrate their effectiveness. Already the movement is directing tens of millions of dollars to charities that are effectively reducing the suffering and death caused by extreme poverty.

Second, effective altruism is a way of giving meaning to our own lives and finding fulfillment in what we do. Many effective altruists say that in doing good, they feel good. Effective altruists directly benefit others, but indirectly they often benefit themselves.

Third, effective altruism sheds new light on an old philosophical and psychological question: Are we fundamentally driven by our innate needs and emotional responses, with our rational capacities doing little more than laying a justificatory veneer over actions that were already determined before we even started reasoning about what to do? Or can reason play a crucial role in determining how we live? What is it that drives some of us to look beyond our own interests and the interests of those we love to the interests of strangers, future generations, and animals?

Finally, the emergence of effective altruism and the evident enthusiasm and intelligence with which many millennials at the outset of their careers are embracing it offer grounds for optimism about our future.

Effective altruists do things like the following: living modestly and donating a large part of their income—often much more than the traditional tenth, or tithe—to the most effective charities; researching and discussing with others which charities are the most effective or drawing on research done by other independent evaluators; choosing a career in which they can earn most, not in order to be able to live affluently but so that they can do more good; talking to others, in person or online, about giving, so that the idea of effective altruism will spread; giving part of their body—blood, bone marrow, or even a kidney—to a stranger.

What unites all these acts under the banner of effective altruism? The definition that appears in Wikipedia, which is now becoming standard, is “a philosophy and social movement which applies evidence and reason to determining the most effective ways to improve the world.” That definition says nothing about motives or about any sacrifice or cost to the effective altruist. Given that the movement has altruism as part of its name, these omissions may seem odd. Altruism is contrasted with egoism, which is concern only for oneself. But we should not think of effective altruism as requiring self-sacrifice, in the sense of something necessarily contrary to one’s own interests. If doing the most you can for others means that you are also flourishing, then that is the best possible outcome for everyone. Many effective altruists deny that what they are doing is a sacrifice. Nevertheless they are altruists because their overriding concern is to do the most good they can. The fact that they find fulfillment and personal happiness in doing that does not detract from their altruism.

‘Warm glow givers’ are not so interested in whether what they are doing helps others.

Psychologists who study giving behavior have noticed that some people give substantial amounts to one or two charities, while others give small amounts to many charities. Those who donate to one or two charities seek evidence about what the charity is doing and whether it is really having a positive impact. If the evidence indicates that the charity is really helping others, they make a substantial donation. Those who give small amounts to many charities are not so interested in whether what they are doing helps others—psychologists call them warm glow givers. Knowing that they are giving makes them feel good, regardless of the impact of their donation. In many cases the donation is so small—$10 or less—that if they stopped to think, they would realize that the cost of processing the donation is likely to exceed any benefit it brings to the charity.

In 2013, as the Christmas giving season approached, 20,000 people gathered in San Francisco to watch a five-year-old boy dressed as “Batkid” ride around the city in a Batmobile with an actor dressed as Batman by his side. The pair rescued a damsel in distress and captured the Riddler, for which they received the key of “Gotham City” from the mayor—not an actor, he really was the mayor of San Francisco. The boy, Miles Scott, had been through three years of chemotherapy for leukemia, and when asked for his greatest wish, he replied, “To be Batkid.” The Make-A-Wish Foundation had made his wish come true.

Does that give you a warm glow? It gives me one, even though I know there is another side to this feel-good story. Make-A-Wish would not say how much it cost to fulfill Scott’s wish, but it did say that the average cost of making a child’s wish come true is $7,500. Effective altruists would, like anyone else, feel emotionally drawn toward making the wishes of sick children come true, but they would also know that $7,500 could, by protecting families from malaria, save the lives of at least three children and maybe many more. Saving a child’s life has to be better than fulfilling a child’s wish to be Batkid. If Scott’s parents had been offered that choice—Batkid for a day or a complete cure for their son’s leukemia—they surely would have chosen the cure. When more than one child’s life can be saved, the choice is even clearer. Why then do so many people give to Make-A-Wish, when they could do more good by donating to the Against Malaria Foundation, which is a highly effective provider of bed nets to families in malaria-prone regions? The answer lies in part in the emotional pull of knowing that you are helping this child, one whose face you can see on television, rather than the unknown and unknowable children who would have died from malaria if your donation had not provided the nets under which they sleep. It also lies in part in the fact that Make-A-Wish appeals to Americans, and Scott is an American child.

Effective altruists will feel the pull of helping an identifiable child from their own nation, region, or ethnic group but will then ask themselves if that is the best thing to do. They know that saving a life is better than making a wish come true and that saving three lives is better than saving one. So they don’t give to whatever cause tugs strongest at their heartstrings. They give to the cause that will do the most good, given the abilities, time, and money they have.

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Doing the most good is a vague idea that raises many questions. Here are a few of the more obvious ones, and some preliminary answers.

What counts as “the most good”?
Effective altruists will not all give the same answer to this question, but they do share some values. They would all agree that a world with less suffering and more happiness in it is, other things being equal, better than one with more suffering and less happiness. Most would say that a world in which people live longer is, other things being equal, better than one in which people have shorter lives. These values explain why helping people in extreme poverty is a popular cause among effective altruists. A given sum of money does much more to reduce suffering and save lives if we use it to assist people living in extreme poverty in developing countries than it would if we gave it to most other charitable causes.

Does everyone’s suffering count equally?
Effective altruists do not discount suffering because it occurs far away or in another country or afflicts people of a different race or religion. They agree that the suffering of animals counts too and generally agree that we should not give less consideration to suffering just because the victim is not a member of our species. They may differ, however, on how to weigh the type of suffering animals can experience against the type of suffering humans can experience.

Does the idea of doing the most good mean that it is wrong to give priority to one’s own children? Surely it can’t be wrong to put the interests of family members and close friends ahead of the interests of strangers?
Effective altruists can accept that one’s own children are a special responsibility, ahead of the children of strangers. There are various possible grounds for this. Most parents love their children, and it would be unrealistic to require parents to be impartial between their own children and other children. Nor would we want to discourage such bias because children thrive in close, loving families, and it is not possible to love people without having greater concern for their well-being than one has for others. In any case, while doing the most good is an important part of the life of every effective altruist, effective altruists are real people, not saints, and they don’t seek to maximize the good in every single thing they do, 24/7. Effective altruists typically leave themselves time and resources to relax and do what they want. For those of us with children, being close to them and other family members or friends is central to how we want to spend our time. Nonetheless, effective altruists recognize that there are limits to how much they should do for their children, given the greater needs of others. Effective altruists do not think their children need all the latest toys or lavish birthday parties, and they reject the widespread assumption that parents should, on their death, leave virtually everything they own to their children rather than give a substantial part of their wealth to those who can benefit much more from it.

What about other values, such as justice, freedom, equality, and knowledge?
Most effective altruists think that these other values are good because they are essential for building communities in which people can live better lives, free of oppression, and have greater self-respect and freedom to do what they want as well as experience less suffering and premature death. No doubt some effective altruists hold that these values are also good for their own sake, independently of these consequences, but others do not.

Does promoting the arts count as improving the world?
In a world that had overcome extreme poverty and other major problems that face us now, promoting the arts would be a worthy goal. In the world in which we live, however, donating to opera houses and museums isn’t likely to be doing the most good you can. When the entertainment mogul David Geffen gave $100 million for the renovation of the Avery Fisher Hall at New York’s Lincoln Center (now to be renamed David Geffen Hall) he could have found better things to do with his money.

Is it really possible for everyone to practice effective altruism?
It is possible for everyone who has some spare time or money to practice effective altruism. Unfortunately, most people who give to charity do not compare the effectiveness of the various charities to which they might donate. Even professional philanthropy advisors are likely to tell their clients to “follow their passion.” In an online leaflet called “Finding your Focus in Philanthropy,” Rockefeller Philanthropy Advisors states flatly that there is “obviously” no objective answer to the question of what is the most urgent cause. But we should not embrace relativism about the choice of charity. Even if deciding on the very best cause is extremely difficult, some causes are objectively better than others, and philanthropy advisors ought to be bold enough to say so. Nevertheless, it isn’t likely everyone will become an effective altruist anytime soon. The more interesting question is whether effective altruists can become numerous enough to influence the giving culture of affluent nations. There are some promising signs that this may be starting to happen.

What if one’s act reduces suffering, but in order to act one must lie or harm an innocent person?
In general, effective altruists recognize that breaking moral rules against killing or seriously harming an innocent person will almost always have worse consequences than following these rules. Even thoroughgoing utilitarians, who judge actions to be right or wrong entirely on the basis of their consequences, are wary of speculative reasoning that suggests we should violate basic human rights today for the sake of some distant future good. They know that under Lenin, Stalin, Mao, and Pol Pot, a vision of a utopian future society was used to justify unspeakable atrocities, and even today some terrorists justify their crimes by imagining they will bring about a better future. No effective altruist wants to repeat those tragedies.

Suppose I set up a factory in a developing country, paying wages that are better than local workers would otherwise earn and enough to lift them out of extreme poverty. Does that make me an effective altruist, even if I make a profit?
What are you going to do with your profits? If you decided to manufacture in the developing country in order to make it possible for people to escape extreme poverty, you will reinvest a substantial part of your profits in ways that help more people escape extreme poverty. Then you are an effective altruist. If, on the other hand, you use your profits to live as luxuriously as you can, the fact that you have benefited some of the poor is not sufficient to make you an effective altruist. There are all kinds of intermediate positions between these two extremes. Reinvesting a substantial part of your profits to help more people earn a decent income, while retaining enough to live at a much better level than your employees, puts you somewhere on the spectrum of effective altruism—you are living at least a minimally decent ethical life, even if not a perfect one.

What about giving to your college or university? You teach at Princeton University, and your book The Most Good You Can Do (2015) is based on lectures you gave at Yale University, thanks to the generous gift of a Yale alumnus. Do you deny that giving to such institutions counts as effective altruism?
I count myself fortunate to be teaching at one of the finest educational institutions in the world. This gives me the opportunity to teach very bright, hardworking students like Matt Wage, who are likely to have a disproportionately large influence on the world. For the same reason, I was pleased to accept the invitation to give the Castle Lectures at Yale. But Princeton has an endowment, at the time of writing, of $21 billion, and Yale’s is $24 billion. At the moment there are enough alumni donating to these universities to ensure that they will continue to be outstanding educational institutions, and the money you donate to one of them could probably do more good elsewhere. If effective altruism ever becomes so popular that these educational institutions are no longer able to do important research at a high level, it will be time to consider whether donating to them might once again be an effective form of altruism.

How do effective altruists decide where their donations will do the most good?
The quality and availability of research on the effectiveness of individual charities has risen dramatically over the past few years, largely due to the existence of GiveWell, a research organization set up in 2007 precisely to fill the vacuum that existed previously. The outcome of this research is freely available online. Other organizations, such as The Life You Can Save (which I founded after the publication of a book with that title) draw on GiveWell’s research but broaden the criteria for recommending a charity. Choosing between different causes (for example, global poverty, reducing animal suffering, protecting the environment, reducing risks of human extinction) is the subject of vigorous discussion on websites associated with effective altruism.

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There has long been skepticism about whether people can really be motivated by an altruistic concern for others. Some have thought that our moral capacities are limited to helping our kin; those with whom we are, or could be, in mutually beneficial relationships; and members of our own tribal group or small-scale society. Effective altruism provides evidence that this is not the case. It shows that we can expand our moral horizons, reach decisions based on a broad form of altruism, and employ our reason to assess evidence about the likely consequences of our actions. In this way it allows us to hope that we will be able to meet the ethical responsibilities of a new era in which our problems will be global as well as local.