If you have the capacity to affect other people, there seem to be three basic ways to decide what to do–and then to assess how much good you’ve done once you’ve acted.

1. You can talk to the people affected. You can consult your fellow citizens or even convene them to deliberate and decide together. The advantages include sensitivity to a wide range of perspectives and considerations, from justice to practicality; nuance and complexity; and the chance for people to learn and enrich their individual views. Asking people to assess and influence the policy also honors their dignity and agency. On the other hand, actually asking very large numbers of people to deliberate and decide everything is prohibitively difficult and expensive. Consulting samples of people fails to enhance the agency of everyone else. Further, discussions are subject to serious and pervasive flaws, such as cognitive biases, inequalities of power and influence, tyranny of the majority, and vulnerability to manipulation and strategic action.
2. You can predict and empirically assess the impact of what you do. You can use scientific methods to make predictions and test causal hypotheses. Science incorporates safeguards against biases, such as random sampling and blind review. It’s much more likely than deliberation to predict accurately what will happen if you do something. But it cannot determine whether your methods or your goals are good ones. And it confers power on experts (or employers of expertise) in ways that can be problematic.
3. You can observe price signals. If milk is selling for more than the price of producing it, then people must want milk, and providing it meets a need. The feedback from prices is immediate; it reflects many people’s knowledge, choices, and agency; it’s hard to manipulate; and it allows comparisons. Since you are responsible for allocating finite resources among all possible purposes, prices give you a common metric. One evident drawback  is inequality. For example, market prices would suggest that there’s weak demand for clean water, even though 2.1 billion people lack access to it. They have too little money to affect prices. However, if you are concerned with justice, you can adjust price signals for equity. For instance, you can give poor people money and let them decide how to spend it, instead of dictating their choices. The other major problem with price signals is that they fail to make moral distinctions. Methamphetamine and antibiotics both have prices. It takes a combination of science (to assess affects) and deliberation (to discuss values) to determine that antibiotics are good while meth is bad.

All sectors of a modern society use all three methods. But I would argue that democratic governments are particularly obliged and well-suited to use deliberation. The fact that every citizen has a vote reflects: 1) the equal right of each person to affect outcomes, and 2) the obligation of every citizen to learn and discuss before making choices. For that reason, governments have formed parliamentary bodies and courts that are supposed to deliberate, they have safeguarded free speech, and they have built ways of consulting publics. Unlike a discretionary decision by a private entity, a government program must be subject to public deliberation because it is the people’s government.

Nonprofit associations and philanthropies use discussion and price-signals. But they are particularly well suited to use “science” (in its broadest form, including ad hoc experimentation and program evaluation). The fact that there are large numbers of modest-sized nonprofits and donors means that each one can try different things and observe the effects without accumulating dangerous amounts of power and influence. When their experiments work, others can pick them up. And unlike for-profit firms, they can ignore price signals in order to pursue goals that they believe in for moral reasons. This is why program evaluation is so common in the non-profit sector, whereas major governmental decisions–even massive tax cuts or wars–are hardly ever subject to formal evaluation.

Companies, obviously, use price-signals. If Toyota can’t sell enough Corollas at a profit, it will realize it must change its business. If it observes that Subaru is more profitable, it will consider copying Subaru. However, it’s worth noting that prices offer insufficient guidance even for profit-maximizing firms. Again, assume that Toyota suddenly cannot sell enough Corollas. It must find out why not, and that will probably require some combination of asking people what they value and studying causes and effects–the same techniques used by democratic governments and philanthropies.

Among people committed to democracy and/or philanthropy, prices provoke unease. When something previously offered free is charged for, critics will complain of “neoliberalism” and “marketization” or “commodification.” But if that good was scarce and provided to some group without a charge, then someone must have decided to allocate resources for that purpose and to that group (instead of to something and someone else). Those who make such decisions are morally responsible for exercising their power well. They should strive to determine whether their choices benefit the world. Consultation and science are two means for that purpose, but both have limitations. Prices are also very useful for determining demand and for making comparisons. Not only should responsible people notice prices, but they should worry about whether their actions (through governments and philanthropies) are distorting price signals in ways the deprive them of useful information about other people’s needs. For instance, if you offer free tuition, you can no longer tell whether schooling is what people want.

On the other hand, prices certainly do not offer all the necessary and relevant information, even for people and firms that want to make a profit–and still less for people who pursue justice.