Imagine you play a game. You are given $10 that you can share with another anonymous person or keep for yourself. What will you do? The economic standard of rational self-interest suggests you should keep the money. After all, you don’t know the other person, they don’t know you and, most importantly, they will never know it was you who took the money. However, you may have considered sharing the money, maybe a third or maybe even a half. If you did, you acted in line with a vast body of research by Nobel Prize–winning economists and psychologists revealing that most people are predictably irrational.

Despite these scientific insights, mainstream politicians continue to frame their messages in terms of rational self-interest. They emphasize how a policy may benefit voters personally, downplaying any benefits for the common good. Just recently, political leaders in British Columbia promoted a carbon taxation policy by emphasizing that citizens would get more money back due to income tax cuts and rebates funded from carbon tax revenues: Carbon taxation is in your personal interest. Vote for it!

Why do politicians and marketers pitch policies and products in ways that assume that people are concerned about rational self-interest? One possibility is that the general public may understand rationality better than their choices in scientific experiments suggest. However, they may discount rational interests in favor of another normative standard of judgment, called reasonableness. We explore this possibility in our recent research.

Let’s return to the game above, called a “dictator game.” As a person in charge of the money, you can act as a self-interested dictator who takes it. But people often share with another player because they deem it unfair not to do so; they are guided by a reasonable social norm rather than rational self-interest. On the surface, the distinction between reasonableness and rationality seems like hairsplitting; Latin ratio means to reason. Nevertheless, for moral philosophers these concepts have different flavors: Rationality concerns a decontextualized focus on the individual, the pursuit of personal goals; reasonableness concerns a pragmatic balance of personal goals with fairness.

Do laypeople differentiate between these scholarly standards? If they do, deviations from rational self-interest in situations like the dictator game may reflect a preference for reasonableness. At the same time, appeals to rational self-interest when gathering support of civic projects in politics may be overlooking the opportunity to inspire the public by appealing to their sense of civic reasonableness rather than their self-interested rationality.

We asked people to play the dictator game described above, instructing them to act rationally or to act reasonably. Instructions to “be rational” led to largely self-serving decisions; most people decided not to share anything or to share just a little. In contrast, instructions to “be reasonable” promoted fairer, socially conscious choices, with most people sharing a half. Moreover, people who described themselves as rational were unlikely to share anything, but people who described themselves as reasonable were more likely to share a half.

This difference between rational and reasonable judgments occurred both in North America and in Pakistan, where we measured behavior among bankers, street merchants and even residents in remote villages. It also generalized across economic games, including the prisoner’s and commons dilemma games. In each case, people expected rational persons to be self-interested and reasonable persons to pragmatically balance self-interest with fairness to others.

Differences between rationality and reasonableness also extend to the language people use on the news, on TV, and in books covering languages spoken in one sixth of the world today. In each case, rationality is represented as individual-focused, analytic and abstract, linked with words such as “self-interest,” “agent” and “numbers.” In contrast, reasonableness is represented as communal, pragmatic, and context-sensitive, linked with words such as “care,” “degree” and “accommodation.”

Our work indicates that people have a better understanding of rational self-interest than assumed by economists and psychologists. However, despite understanding what it takes to be rational, people often prefer to be irrationally reasonable. In other words, people may use a different standard to figure out what to do than the standard of rational self-interest favored by economists and mainstream politicians.

The discovery that most people recognize reasonableness as a distinct and often preferred standard for judgment suggests an opportunity to enrich public discourse by framing more political messages in terms of reasonableness—by emphasizing civic, socially conscious rationales for those policies rather than solely emphasizing rationally self-interested considerations.

For example, the British Columbia politicians who were promoting a carbon tax may have been more successful if they had emphasized how the tax was a way of fulfilling a responsibility to future generations rather than trying to convince voters that the tax would benefit their own finances. Appealing to the public’s sense of reasonableness may also help to reanimate the marginalized and disenfranchised segments of the public.

Our work also casts decades of research in psychology and economics in a new light. We think that the idea of people being hopelessly irrational is misguided. We question whether the primary way to avoid irrational behavior requires “nudging” people towards choosing a more rational option as a default strategy. Instead, our research indicates that people may choose to be irrational when their rational self-interest violates their preferred standard of reasonable conscious behavior.

Cultural critics such as Stephen Toulmin have raised concerns that the nuanced relationship of rationality and reasonableness has been undone by an influential neoliberal ideological movement in the late 20th century that has championed the economists’ model of rational self-interest as the only standard for sound judgment. Our research contradicts such claims. The successful spread of the economic ideals of rational self-interest has not eliminated people's commitment to the reasonableness standard.

The distinction between rationality and reasonableness in moral philosophy and the law runs deep. Our research suggests it is also meaningful in daily life. Giving one’s spouse cash for his or her birthday is rational, but it isn't reasonable. Telling your parents to stay at a hotel instead of your guest room may be rational, but it isn't necessarily reasonable. Or, to paraphrase George Bernard Shaw, it is rational to strive for adapting the world to oneself, though it's unreasonable to do so.