What Is Friendship? Definition, Traits, and Why It Matters

What Is Friendship? A Definition

Friendship is a voluntary, informal relationship based on reciprocity and emotional closeness between two people, typically without a sexual component. These five criteria come from relationship-psychology research by Wrzus, Zimmermann, Mund & Neyer (2017) and are summarized in the overview by Neyer and Wrzus (2018).

At its core, friendship differs from other relationships through a triad: voluntariness, informality, and emotional depth. You choose your friends yourself — unlike family, which is given, or colleagues, who are determined by the work context. And when a friendship has run its course, it can be dissolved independently — without legal or social ties.

Sociology adds an important perspective: friendship is not institutionalized(Schobin et al., 2016). There is no registry office, no contract, no ritual that officially establishes a friendship. It lives entirely on the efforts of those involved. That makes it simultaneously fragile and valuable — because every friendship that exists does so because both sides actively choose it.

A philosophical accent comes from Leibowitz (2018): he defines friendship as a relationship in which each person values the other and successfully communicates that appreciation through shared activities. Mere goodwill is not enough — it must be recognized as such.

Behavioral biology offers an entirely different approach: Brent et al. (2014) define friendship as bidirectional, affiliative interactions whose frequency and consistency distinguish them from non-friendships. This definition deliberately avoids assumptions about feelings or motives and enables cross-species comparisons — because friendship also exists among chimpanzees, dolphins, and elephants.

What all perspectives share: friendship is not a state but an active process. It does not arise from a decision but from repeated interaction — and it fades when that interaction stops.

Five Traits of True Friendship

Five empirically validated criteria distinguish friendship from all other social relationships. All five must work together — if one is missing, researchers tend to speak of acquaintanceship, collegial ties, or romantic relationships (Neyer & Wrzus, 2018).

Voluntarinessis the trait that most clearly separates friendship from family relationships. You cannot choose your parents — but you decide whom you trust, whom you call, and whom you open up to. This freedom of choice makes friendship a relationship form in its own right, one that no other can replace.

Reciprocity— the mutuality of affection and support — sounds obvious but is not. In an analysis of 84 school networks, Ball & Newman (2013) found that only 30–50% of friendship nominations are actually reciprocated. Many relationships we perceive as friendships are classified differently by the other side. More in our article on reciprocity in friendships.

A crucial finding corrects the intuitive assumption: it is not actual reciprocity that determines friendship quality but perceivedreciprocity. Whether two friends objectively support each other equally matters less than whether both feel the relationship is balanced (Neyer, Wrzus, Wagner & Lang, 2011).

Emotional closeness is the glue that holds all other traits together. It shows in familiarity, in positive feelings for each other, and in the willingness to be vulnerable. Argyle and Henderson (1984) empirically identified this dimension as the central difference between active and ended friendships.

Aristotle and the Types of Friendship

The oldest systematic friendship theory comes from Aristotle. In the Nicomachean Ethicshe distinguishes three basic types by the quality friends value in each other — and this tripartition has lost remarkably little relevance over 2,300 years.

1. Virtue friendship— the highest form. Both friends admire the other’s inner virtue (arete): their character, integrity, and values. Because virtues are stable and endure in times of crisis, this friendship is particularly lasting. In it, one sees the friend as an “other self” — they extend one’s own identity. Cooper (1977) puts it succinctly: through the friend one gains an “objective view of oneself.”

2. Pleasure friendship— the friends value each other because time together is enjoyable. The friend is witty, entertaining, a good conversationalist. When the pleasure changes, the relationship falters.

3. Utility friendship— both sides benefit practically: through business connections, recommendations, or mutual help. These relationships are the most fragile because they end as soon as the mutual benefit disappears.

The three types often overlap. Even virtue friendship contains elements of pleasure and utility. What matters is the hierarchy: you must find the friend useful and pleasant becauseyou value them as a person — not the other way around. Valuing a friend only for their utility reduces them to an instrument.

An important note on scope: the Greek philiais broader than our modern word “friendship.” Aristotle includes family relationships, fellow citizens, and business contacts. Within this broad spectrum he places virtue-based friendship among equals at the top. Sherman (1987) emphasizes that friendship provides the “context for the expression of virtue and ultimately for happiness.” More on the tripartition and its modern relevance in our article on Aristotle’s three types of friendship.

The limits of this classification are obvious: Aristotle restricts the highest friendship to equal, virtuous adults — meaning exclusively free men of Greek society. Women, slaves, and children were excluded. Modern definitions therefore place greater emphasis on emotional closeness and voluntariness than on virtue.

Rules of Friendship

Friendships have no formal rules — but they are far from rule-free. In a comprehensive study, Argyle and Henderson (1984) tested 43 potential friendship rules on British samples. 21 were rated as important. But only six rules passed all four validation criteria simultaneously.

The four criteria were: high agreement in the overall sample, distinguishing between active and ended friendships, attribution as a cause of friendship dissolution, and distinguishing between high and low friendship quality.

The six validated core rules are:

1. Stand up for your friend when they are not present
2. Share good news with your friend
3. Show emotional support
4. Trust each other and confide in each other
5. Offer help voluntarily when needed
6. Make an effort to ensure shared time is enjoyable

In terms of content, these rules mostly belong to the categories of exchange and intimacy rules. They concern the reciprocity of support and the deepening of emotional closeness. General rules like “respect privacy” or “don’t criticize publicly” were also strongly endorsed, but they do not specifically distinguish friendships from other relationships.

Gender differences emerged mainly in intimacy rules: women emphasized emotional support, intimate conversations, and expressions of affection significantly more than men. Men, in turn, more often cited excessive teasing as a reason for a friendship ending. More detail in our article on the unwritten rules of friendship.

A sober finding with far-reaching implications: if you want to know whether a friendship is stable, do not check the feeling — check whether these six behaviors are present. Rules do not replace feeling, but they make it visible and measurable.

Friendship and Happiness

That friendship makes us happy sounds trivial. The mechanism behind it is not. Leibowitz (2018) argues that friendship contributes to happiness because it boosts self-esteem— through three sequential steps.

First, friends valueeach other — they recognize the other’s worth as a person. Second, they communicatethat appreciation successfully, for example through shared activities, self-disclosure, or engaging with the other’s interests. Third, others’ evaluations influence our own self-evaluation — those seen as valuable by a friend develop a stronger sense of self-worth.

This model also explains the universality of friendship: since all people seek happiness and friendship is the most accessible way to experience mutual appreciation, people in all cultures seek friendships. More in our article on friendship and happiness.

Empirical research confirms the philosophical approach with hard numbers. A meta-analysis by Holt-Lunstad, Smith & Layton (2010) with N = 310,000showed that close friendships are the strongest predictor of survival — stronger than diet, exercise, or BMI. Only tobacco use reaches a comparable effect size.

For Germany the numbers are alarming: 46% of 16- to 30-year-oldsreport feeling lonely (Bertelsmann Stiftung, 2024). Before the pandemic the share was 14–17%. In 2020 it jumped to 41% and by 2022/23 had only dropped to 36%. Social loneliness (39%) is more common than emotional loneliness (29%). Anyone who considers friendship a “nice-to-have” underestimates its impact on health.

Leibowitz describes friendship as an instrumental final value: it is valued for its own sake, but its value lies in contributing to happiness. This is not a contradiction — it means that friendship is not a luxury but a basic need. Aristotle put it unmistakably: “No one would choose to live without friends — even if they possessed all other goods.”

Limits of the Definitions

The five core traits work better in theory than in practice. The boundaries between relationship types are fluid. According to data from the German Federal Statistical Office (2012), nearly two thirds of employees in Germany say they have good friends at work. Such relationships are formally shaped by the work role but functionally close to friendships.

The boundary to romantic relationships is similarly blurred — historically, friendship and romantic love were hardly distinguished until the 18th century. And the question of whether digital relationships qualify as true friendships is debated in philosophy.

Most definitions come from Western, individualized societies. Whether the five criteria apply equally in collectivist cultures is insufficiently researched. What the research does allow is this statement: friendship is not a category with sharp edges but a spectrum— and the five traits mark the core of that spectrum, not its boundaries.

Key Takeaways

Friendship is not a vague category but an empirically describable phenomenon with five core traits, validated behavioral rules, and measurable effects on health and happiness. The research shows three things simultaneously:

1. Friendship is voluntary, informal, reciprocal, emotionally close, and non-sexual — all five traits together distinguish it from every other relationship type
2. Six concrete behavioral rules keep friendships alive — from loyalty and emotional support to sharing successes
3. Friendship is not a nice-to-have but a health factor on the scale of exercise and diet — supported by meta-analyses with over 310,000 participants

The most practical insight: friendship thrives on interaction, not on feeling alone. The rules show that it is concrete actions — standing up, sharing, supporting, trusting, helping, enjoying — that define a friendship. Not what you feel but what you do.

Frequently Asked Questions

What is friendship in simple terms?

Friendship is a voluntary, informal relationship between two people based on mutual affection, trust, and emotional closeness. Unlike family or work relationships, friendship is freely chosen and can be ended independently at any time — without legal or social consequences (Wrzus et al., 2017).

What are the most important traits of a friendship?

Research identifies five core traits: voluntariness, informality, reciprocity, emotional closeness, and the absence of a sexual component. All five must work together — if one is missing, it is more likely an acquaintanceship, a collegial relationship, or a romantic relationship (Neyer & Wrzus, 2018).

How many real friends does the average person have?

Studies show that most people have about five close friends — the so-called innermost Dunbar layer. Surprisingly, only 30–50% of friendship nominations are actually reciprocated. Many relationships we perceive as friendships are classified differently by the other side (Ball & Newman, 2013).

What distinguishes friendship from acquaintanceship?

The key difference lies in emotional depth and experienced reciprocity. Acquaintances share a context — neighborhood, workplace, club — but not the emotional closeness and trust that define friendships. Stricter reciprocity rules also apply: when the balance is disrupted, the relationship ends more quickly than among close friends.