The word “nice” has an unusual history in the English language.

Originally a term for “foolish”, its meaning over the centuries has morphed from “wanton” to “reserved” to “fastidious”. These days, it has become a somewhat bland and opaque description of personality: “she’s really nice.”

But its common usage hints at the characteristics that matter deeply to us.

Personality psychology can help unsnarl some of these fuzzy concepts. Recent research suggests that our tendency to be “nice” can be separated into two related but distinct personality traits: politeness and compassion.

We see these differences play out in social decision making, where politeness is linked to being fair and compassion to helping others.

A tale of two traits

Decades of research have shown that personality traits describing how well we treat others are often observed together. These are summarised by the term agreeableness, one of five broad dimensions capturing the majority of human personality.

Some of our most valued qualities — kindness, integrity, empathy, modesty, patience, and trustworthiness — are nestled within this dimension. They are instilled in us at an early age and reflect important standards through which we judge others and ourselves.

But are there exceptions to this cluster of “nice” personality traits? What about your big-hearted but foul-mouthed friend, or a well-mannered but distant acquaintance?

It turns out that agreeableness can be meaningfully divided into two narrower traits. Politeness refers to our tendency to be respectful of others versus being aggressive. It’s about good manners and adhering to societal rules and norms — what we’d see in upstanding, decent folks, or “good citizens”, if you will. In contrast, compassion refers to our tendency to be emotionally concerned about others versus being cold-hearted — what we’d see in the proverbial “good Samaritan”.

Clearly, these two characteristics often go hand in hand, but they also diverge from one other in interesting ways. For example, studies on political ideology show that politeness is associated with a conservative outlook and more traditional moral values, while compassion is associated with liberalism and progressive values.

One view is that politeness and compassion are linked to different brain systems — politeness with those governing aggression, and compassion with those regulating social bonding and affiliation. We see some evidence for this in neuroimaging research, where compassion — not politeness — is related to structural differences in brain regions involved in empathic responses.

Politeness and compassion in economic games

Our research has examined how politeness and compassion translate into different kinds of behaviours. We did this using social decision-making tasks called economic games, which involve fairness, cooperation, and punishment.

Economic games have a long history in behavioural economics and evolutionary biology, where they have helped debunk assumptions of human selfishness with evidence for our altruism.

But can altruism in these games be explained by people’s politeness, compassion, or both?

We began with the dictator game, a task in which a person is asked to divide a fixed sum of money with an anonymous stranger. Our results showed that traditional economic predictions were wrong on two counts. Not only did people not behave selfishly, they behaved in different ways depending on their personality.

Notably, polite people were more likely to split the money fairly than their rude counterparts. Surprisingly, we did not see this for compassion, which may indicate that sharing money with a stranger doesn’t necessarily arouse emotional concern.

But what if that stranger is actually in need of help? We studied this kind of scenario using a third-party recompensation game. In this task, a person observes an unfair division of money between two people and is given the chance to donate their own money to the victim.

Here, compassionate people gave away more money than their cold-hearted counterparts. Polite bystanders were not selfish per se — we know this because they were willing to part with their money in the dictator game just moments earlier. But they were no more likely than anyone else to intervene when bearing witness to the mistreatment of others.

These studies highlight some crucial differences between good citizens and good Samaritans. Polite people don’t necessarily help those in need, but they are fair-minded and peaceable. Meanwhile, compassionate people aren’t necessarily even-handed and rule-abiding, but they are responsive to the misfortunes of others.

What kind of ‘nice’ should we be?

In light of growing evidence that our personality can be changed, should we be trying to cultivate our politeness or our compassion?

Our capacity to empathise with others is often hailed as the key to healing social divisions. And while excessive politeness sometimes gets a bad rap, consider how easily society would descend into conflict if people acted aggressively and exploitatively, eschewing basic social rules.

Ultimately, good citizens and good Samaritans each have a role to play if we are to get along with others. Perhaps politeness and compassion are best captured in the principle:

If you can, help others; if you cannot do that, at least do not harm them.

Personality research suggests that although these twin virtues stem from separate strands of human nature, we can strive for both.