When Two Become One: The Self-Expansion Theory of Love

At Marriage Pact, we know that the saying “opposites attract” holds little water when it comes to initial attraction—and especially when it comes to what makes great relationships last. But this isn’t always true.

Similarity’s advantage only really applies to the big things, which are what we match people on when they answer our questions. These include the core aspects of the self in the context of relationships: personality, basic values, romantic tendencies, and future goals—the constructs we hit on in our research-backed theoretical model of what matters in long-term relationships. 

But once you share these baseline similarities, there’s room for acceptable differences. Differences in interests, hobbies, and even childhood experiences can actually be helpful when it comes to building a relationship—and that’s thanks to the self-expansion model of love. Let’s discuss.

The self-expansion model of love, proposed by Arthur and Elaine Aron in 1986, is based on two ideas:

  1. People are motivated to “expand the self” — anything anyone does in life is in service to the ultimate goal of evolving one’s self-concept by acquiring new resources, perspectives, and identities.

  1. People mainly achieve this by mentally including close others in the self — when you become close with somebody, you are effectively folding in their self-concept with yours, thereby merging the two into one giant mega-self. Crazy.

According to this model, the “acceptable differences” from earlier are actually essential to the expansion of the self, which (again, according to the model) is basically the goal of life. 

Those of us with close others can probably attest to the idea that it’s easy to confuse the “I” with the “we.” In fact, Aron and Aron experimentally proved this to be true in a 1991 study with three different procedures. This “identity fusion” in pair-bonding might be scary news for people who are high in attachment avoidance, but it’s actually good for our relationships to be so intertwined. 

This enmeshment happens naturally when you enter a new relationship and can even explain the “honeymoon phase” for most new couples, where there’s a heightened period of strong romantic motivation and satisfaction thanks to the rapid rate of self-expansion. 

It also provides a (non-chemical) explanation for why and how the honeymoon phase ends—after a while, the rate at which your partner can help you self-expand naturally decreases as you become more familiar with each other. Boo.

However, not all is lost! Just as the self-expansion theory can explain decline in relationship satisfaction over time, it offers direction for how to build it back up again. If you each take the time to acquire new resources, perspectives, and identities through other means (say, through a friend, or … the Internet), sharing these new differences and experiences with each other can offer another dose of the self-expansion we all crave. 

So, it’s true that opposites might attract… but only inasmuch as they provide an opportunity to create similarities. Try capitalizing on your loved one’s differences while sharing your own—and you’ll get the double benefit of improving yourself and the relationship (don’t forget, they’re the same!).