How Friendships Form: The Science of Getting to Know People

How Do Friendships Form?

Friendships follow a multi-stage process: proximity creates opportunity, the mere-exposure effect builds familiarity, homophily (similarity) filters potential friends, and self-disclosure deepens the relationship. Each step builds on the one before it.

Fehr (2008) groups the research into three categories of factors: situational factors (proximity, frequency of contact), individual factors(personality, social skills), and dyadic factors (similarity, complementarity, reciprocity). The strongest predictors are situational and dyadic in nature.

Proximity as a Catalyst

The classic evidence comes from Festinger, Schachter, and Back (1950): in student dormitories, residents were more likely to befriend those whose rooms were closer. What mattered was not physical distance alone but functional distance — the layout of stairs and corridors determined how often people ran into each other.

Nahemow and Lawton (1975) confirmed this in a public housing project: 88% of the closest friendships were within the same building. Notably, friendships between people of different ages or backgrounds existed almost exclusively among immediate neighbors — proximity bridged dissimilarity.

Even brief proximity is enough: Back, Schmukle, and Egloff (2008) showed that first-year students randomly seated next to each other in an orientation session were more likely to become friends later. The seating was entirely random.

The Mere-Exposure Effect

The more often we encounter someone, the more we tend to like them — even without direct interaction. This mere-exposure effect was first systematically demonstrated by Zajonc (1968) and is one of the most reliable findings in social psychology. Hundreds of studies confirm: repeated exposure alone increases liking (Bornstein, 1989).

An important caveat: when the initial impression is negative, repeated contact can reinforce dislike rather than soften it. The mere-exposure effect only works when there is no initial aversion.

Similarity Attracts

Homophily— the tendency to befriend similar people — is one of the most robust findings in friendship research. McPherson, Smith-Lovin, and Cook (2001) showed in a foundational paper: similarity in age, gender, education, ethnicity, and values is the strongest predictor of who becomes friends with whom.

Gitmez and Zarate (2022) provided a field experiment at Peruvian boarding schools: randomly assigned neighboring students were 16.6 percentage pointsmore likely to be friends. Particularly revealing: the proximity effect was significantly stronger for dissimilar pairs — proximity and similarity act as substitutes. More on this in the article on similarity and friendship.

Opening Up: Self-Disclosure

Self-disclosure marks the transition from acquaintance to friendship. Altman and Taylor (1973) described the process with their Social Penetration Theory: relationships deepen as conversation topics become broader and more intimate — from the superficial to the personal.

Aron et al. (1997) showed experimentally: pairs who asked each other 36 increasingly personal questions felt closer after 45 minutes than control pairs making small talk. Reciprocal self-disclosure — opening up to each other — is the key.

This ties into Leibowitz’s concept of communicating appreciation: opening up signals trust and appreciation. Responding in kind reciprocates both.

Activities That Bond

Friendships need shared time — but not all shared time is equally effective. Activities that release endorphins — laughing, singing, dancing, exercising together, sharing meals — strengthen friendships biochemically more than passive togetherness.

Jeffrey Hall estimates that about 200 hours of shared time are needed to go from acquaintance to close friend. 50 hours for the first step from acquaintance to friend, 90 for a good friend. These numbers underscore: friendship requires regular investment, not a single intense moment.

Research Limitations

Most studies come from university settings with predominantly young adults. Whether the same formation mechanisms apply equally in other life stages is less well studied. In the age of digital communication, the question also arises whether online contacts weaken the proximity effect.

Opportunity structures and similarity are mutually reinforcing: future friends meet at university because similar education and interests led them down the same path. The direction of causality is not always easy to disentangle.

Frequently Asked Questions

How do friendships form?

Through the interplay of three factors: physical proximity creates opportunities, repeated contact (the mere-exposure effect) builds familiarity, and similarity in age, education, and values deepens the bond. Self-disclosure marks the transition from acquaintance to friend.

How do I make new friends?

Create regular opportunities for encounters: clubs, classes, volunteer work. Research shows it takes about 200 hours of shared time to move from acquaintance to close friend. What matters is consistency, not the intensity of any single meeting.

What fosters friendships?

Three main factors: proximity (physical closeness), homophily (similarity in demographic and psychological traits), and reciprocity (mutual affection). All three are broadly supported by evidence — from Festinger (1950) to recent field experiments.

How long does it take for a friendship to form?

About 50 hours of shared time to go from acquaintance to friend, 90 hours for a good friend, and 200 hours for a close friend (Hall, 2019). These numbers underscore that friendship takes time and repeated interaction — not a single intense moment.