Both frameworks put commitment at the center of a relationship, but they're answering different questions. Here's how the two fit together rather than compete.
Two Different Questions
Sternberg's 1986 triangular theory describes what love is made of: intimacy, passion, and commitment, combining into types like companionate or consummate love. Rusbult's investment model zooms into commitment specifically and explains what predicts it — satisfaction, alternatives, and investment.
Is "Commitment" the Same Idea in Both?
It's the same word pointing at closely related ideas, not identical ones. Sternberg treats commitment as one of three vertices that combine to define a type of love. Rusbult treats it as an outcome with its own separate causes worth unpacking on its own terms.
Using Both Together
- Sternberg's triangle — describes the current mix of intimacy, passion, and commitment in a relationship right now.
- Rusbult's model — explains why the commitment vertex specifically is sitting where it is.
Run side by side, one describes the shape of the relationship, the other explains the mechanics behind one part of it.
Which One Answers "Why Do People Stay?"
Rusbult's model was built specifically for that question and is the stronger tool for it, since it separates investment and alternatives out as forces distinct from how the relationship feels. Sternberg's model is stronger for describing what a relationship IS, rather than why it persists.
Want both readings on your own relationship? Take the free Relationship Commitment Test for the investment-model breakdown, and pair it with the Sternberg Triangular Love Test for the intimacy/passion/commitment shape.
Frequently Asked Questions
What is the core difference between the two models?
Sternberg's 1986 triangular theory describes what love is made of, intimacy, passion, and commitment, combining into types like companionate or consummate love. Rusbult's investment model zooms into commitment specifically and explains what predicts it: satisfaction, alternatives, and investment.
Is commitment the same concept in both theories?
It is the same word pointing at closely related ideas. Sternberg treats commitment as one of three vertices that combine to define a type of love; Rusbult treats it as an outcome with its own separate causes worth unpacking on its own.
Can you use both frameworks on the same relationship?
Yes, they answer different questions well together. Sternberg's triangle can describe the current mix of intimacy, passion and commitment in a relationship, while Rusbult's model explains why the commitment vertex specifically is sitting where it is.
Which one is more useful for understanding why people stay together?
Rusbult's model was built specifically to answer that question and is more predictive on it, since it separates out investment and alternatives as forces distinct from how the relationship feels. Sternberg's model is stronger for describing what a relationship IS, rather than why it persists.