Self-Expansion Theory

Self-Expansion Theory Definition

Close relationships open up new worlds to people. As you interact with roommates, close friends, and relationship partners in college, you will probably start to notice small parts of yourself changing to become a little more like them and vice versa. For example, you might notice that you start taking more interest in sports if you have a partner who always watches basketball and football games on television. Before you know it, you might think of yourself as a sports buff!

Self-Expansion TheoryRelationships can help shape our identities, and they can provide us with shared resources. If your partner owns a car and you do not, you will likely occasionally get a ride to get groceries or go out to dinner. Or if you have a nicer apartment than your partner’s, he or she will likely benefit by spending more time at your place. Besides developing a sense of ourselves and receiving extra resources, we can also develop different perspectives from close relationships. For example, if your partner is from a small town in the Midwest and you are from a large East Coast city, you will likely learn a lot about each other’s worldviews just by interacting and talking.

These changes to people’s identities, resources, and perspectives that occur in relationships are described in and explained by self-expansion theory. Self-expansion theory says that it is very important for people’s sense of self to expand and grow throughout their lives for them to feel satisfied with their lives. Although close relationships can provide us with a rich source of potential expansion, people can experience this type of growth in other ways: through spirituality, creativity, and their interactions with valued objects.

People really enjoy the feeling of self-expansion, and as a result, they try very hard to look for self-expansive opportunities. People can do this in various ways. For example, some people might look for new relationships to keep the positive feeling of growth alive, whereas others might instead try new activities with current relationship partners as a way to increase their self-expansion.

What happens if your best friend bombs a chemistry midterm? Will you react to his or her failure as if it was your own, or will you suddenly want to shrink away from your friend? It makes sense that people include others’ positive elements in their self-concepts when they grow. After all, it usually feels good to have successful friends. However, self-expansion is not necessarily selfish: People don’t only include the good elements of others in themselves when they grow. The fact that some people might even include others’ negative elements in themselves shows how strong the need to self-expand is; it might even be stronger than our need to make ourselves feel good! Finally, like other human motivations, self-expansion is not necessarily a conscious one; a person may not always be aware of why he or she wants to meet new people and try new things.

Self-Expansion Theory Background and History

The motivation to self-expand is tied to people’s ability to accomplish their goals, thus self-expansion is related to psychological models of self-efficacy, intrinsic motivation, self-actualization, and the self-improvement motivation. The idea that the self is created through relationships with close others goes back to Martin Buber’s conception of the “Thou” and “I” uniting and is also related to George Herbert Mead’s work on social interactions. Carl Jung believed that relationship partners could draw out otherwise hidden aspects of the self to create greater wholeness, and Abraham Maslow thought that loved ones could be included in people’s self-concepts. Within social psychology, Fritz Heider’s concept of the unit relation that can form between close others comes closest to Art and Elaine Aron’s recent idea of inclusion of others in the self.

Self-Expansion Theory Research Evidence

One of the most common ways that humans self-expand is through their relationships with others. In relationships, people can feel distant and completely different from the other person, or they can feel a close sense of oneness called psychological overlap. Psychological overlap with close others is measured with the Inclusion of Other in the Self Scale, which is a set of seven pairs of circles with gradually increasing levels of overlap. Participants are asked to select the pair of circles that most represents their relationship.

This scale measures both feelings of closeness and behaviors related to closeness. Psychological overlap as measured by this scale is strongly related to relationship satisfaction, commitment, relationship investment and importance, and the percentage that dating partners use the pronouns we and us when discussing their relationship. This scale also predicts whether people stay in a relationship in a 3-month posttest.

According to research, the idea that the self expands through relationships can be taken literally. For example, people in close relationships describe their self-concepts with more complexity do than those who are not in close relationships. As well, people who report falling in love describe themselves with more different domains of self-content compared with their baseline “not in love” state and compared with those who are not in love.

Relationships high in self-other overlap are characterized by expanded identities, resources, and perspectives from the relationship partner. When the self expands to include another, people may even confuse their own personality traits and memories with close others’ traits and memories. Identity and self-knowledge literally overlap with a highly overlapped other.

In a sense, there is also a literal overlap of resources and possessions with highly overlapped others, perhaps reflecting an awareness of shared outcomes. People treat close others as if they are indistinguishable from themselves: They allocate more resources to close others, giving approximately equal amounts to themselves and their partner when the partner in a money allocation game is a close other but giving more to themselves when the partner is an acquaintance or stranger.

Self-expansion theory also suggests that people may make more situational and less dispositional attributions to explain the behavior of close others, an evaluation more consistent with how information is processed about the self. For example, when your best friend fails on a chemistry test, you will likely consider situational variables that affected your friend’s performance (e.g., having a cold that day) in the same way that you would for yourself, rather than making trait-based attributions as you would for strangers or acquaintances (e.g., they are unmotivated or unintelligent).

Self-Expansion Theory Implications

Self-expansion theory can help provide explanations for both people’s initial attraction to others and the eventual decline in relationship satisfaction that occurs over time. It suggests that one of the main reasons people initially enter romantic relationships is because of the opportunity to self-expand and that attraction is the result of a nonconscious calculation of how much the potential partner can contribute to one’s self-expansion. Extremely high levels of relationship satisfaction that typically occur at the beginning of a relationship are explained by positive feelings resulting from self-expansion, which quickly fade as the two people get to know each other better and opportunities for self-expansion decline. Importantly, the model specifies why relationship satisfaction declines over time and how to increase relationship satisfaction. This has been successfully done in the laboratory through inducing couples to participate in self-expanding activities together (e.g., completing a difficult maze) and in real life by asking couples to spend time doing exciting things together (e.g., learning to dance).


  1. Aron, A., & Aron, E. (1997). Self-expansion motivation and including other in the self. In S. Duck (Ed.), Handbook of personal relationships (2nd ed., pp. 251-270). Chichester, UK: Wiley.
  2. Aron, A., McLaughlin-Volpe, T., Mashek, D., Lewandowski, G., Wright, S., & Aron, E. (2004). Including others in the self. European Review of Social Psychology, 15, 101-132.
  3. Aron, A., Norman, C., & Aron, E. (1998). The self-expansion model and motivation. Representative Research in Social Psychology, 22, 1-13.